Disclaimer:

This is no longer my idea it has become the brainchild of all of the people who posted in this thread (supporter or detractor).  This started out as a cash for trophies proposal and has been shaped by the PSN community into something more reasonable and just as rewarding.  I have changed the OP multiple times to reflect criticisms or suggestions brought up by others.  And the Subject has been changed to be more appropriate as well.  So, if you think you have already read this I implore you to reread the OP and see what has changed.

The Idea: 

SONY would help themselves and gamers by rewarding players for their earned trophies with discounts on future PSN purchases, especially in a recession. 

• By providing people a financial incentive to use the PSN Store, SONY would encourage people to spend their money on virtual stuff for HOME as well as games, movies, and other content from the PSN Store. 
• As a beneficial side effect, PS3 customers might trade-in games a lot later than other gamers because the perceived value of the trophies will have gone up and so will the motivation to get them.  
• This tactic also complements the Ad-based revenue strategy of HOME - because gamers will always be guaranteed to have some money in their PSN accounts to spend, so advertisers will always have a market to sell to. This is a win-win for everybody!

The Details:

Each game's trophies would provide discounts at the store via a redemption code in the following manner.

• Obtaining all bronze trophies unlocks a redemption code worth up to $1 off at the PSN store*.

• Obtaining all bronze AND silver trophies increases the worth of that redemption code to up to $3 off at the PSN store*.
• Obtaining all bronze, silver, AND gold trophies (i.e. earning the Platinum trophy) increases the worth of that redemption to up to $5 off at the PSN store*

* Users cannot combine codes from different games.

** For every $11 the user spends they can use their code to save $1, up to $5 off.

*** Exclusions would apply and would be up to SONY.  They would most likely only let us get a discount on a group of "Featured" items.

The promotion would be open to all gamers.  (It wouldn't matter whether you bought the game new, used, rented it, or borrowed it).

• I originally tried to make this a one coupon per disc solution but that has since been shown to be unreasonable.  I was under the impression that Blu-rays had unique IDs, but it seems that they only have one per title not per disc.
• The money amounts have been widened to the point that SONY makes a profit every time and the user ends up purchasing something that can't be traded in or sold, making the small discount more than worth it for them.
• Getting 100% of trophies takes a lot of time and effort and most likely will only be done by big fans of that game - so this is not like handing out free money for playing games.  This is like the rewards program that any retailer has in place except that it is geared towards gamers.

The Simpler Alternative:

Get $1 PSN credit each time you level, and an extra $2 PSN credit for every 3rd level.  That's almost how GameStop does it and they aren't losing money.  They are raking it in.

• Bronze Trophy: 15 points (1)
  
• Silver Trophy: 30 points (2)
  
• Gold Trophy: 90 points (6)
  
• Platinum Trophy: 180 points (12)
  • GTA is probably the maximum you could get for a full game (51 trophies [42/5/3/1]) = 1230 points
  • LittleBigPlanet (48 trophies [36/8/3/1]) = 1230 points
  • PixelJunk Eden (20 trophies [19/1/0/0]) = 315 points
  • Fat Princess (21 trophies [21/0/0/0]) = 315 points

• Level 1 - 0 pts - Freebie
• Level 2 - 200 pts - At least 1 PSN game 
• Level 3 - 600 pts - At least 1  Full game or 2 PSN games
• Level 4 - 1200 pts - At least 1 Full game or 4 PSN games
• Level 5 - 2400 pts - At least 2 Full games
• Level 6 - 4000 pts - At least 3 Full games
• Level 7 - 6000 pts - At least 5 Full games
• Level 8 - 8000 pts - at least 6 Full games
• Level 9 - 10000 pts - at least 8 Full games
• Level 10 - 12000 pts - at least 10 Full games
• Level 11 - 14000 pts - at least 11 Full games
• Level 12 - 16000 pts - at least 13 Full games
•  Level 13 - 24000 pts - at least 19 Full games
• Level 14 - 32000 pts  - at least 26 Full games

How is this profitable: 

The Traditional Model:

1. Publisher sells AAA game to Retailer (sometimes a distributor may be in the middle) for $48 (wholesale cost)

2. Publisher and Console Manufacturer split the Wholesale cost based on their prior agreement (Usually $40 to the publisher / $8 to SONY). 

3. Retailer sells game at $60 and pockets $12 for their troubles.

Publisher = $40, SONY = $8, Retailer = $12

4a. Gamer plays game and then goes back to Retailer to get a new,different one when they can afford it.  At most SONY makes $8; and in a recession gamers are going to be doing this less frequently than they currently are.

4b. Gamer plays game and then goes back to Retailer to get a used,different one when they can afford it.  At most SONY makes $0; and in a recession gamers are going to be doing this more frequently than they currently are.

Publisher = [$40, $80], SONY = [$8, $16], Retailer = [$24, $67] (best case scenario of buying a used title for $55)

Now's where the proposed incentive plan comes into play

4c. Gamer plays game and then goes on to the PSN Store to use up their earned discount on a full priced game or movies.

5.  Gamer spends at the least $10 of their own money and at most $50 (could be higher if they decide to get stuff at full price).

6.  Sony and Developers split the online cost between 30/70 and 60/40.  In this scenario SONY makes $10.50* {(30% of $55) - $5} on games and movies.   

Publisher = [$47.70, $79.50], SONY = [$10.30, $18.50], Retailer = $12

* The revenue is smaller but the profit is higher if the user purchases HOME items and PSN games instead of a full priced game or movie.

Pros:

• This will drive traffic to the PSN Store and the increased demand will mean better support from developers and content creators.
• In a recession, gamers are going to appreciate any help they can get in affording more games.
• Trophy system will keep this from being an offer that is too generous to be permanent because the majority of people won't unlock all of the trophies
• More users will participate in the HOME economy because they might put their $1 savings towards a piece of furniture or a new outfit instead.
• SONY is not penalizing customers who can't afford to buy new and instead is giving them an incentive to check out the middle priced "new" games on the PSN.
• The PSN will be successful quicker than anyone expects - Analysts don't believe direct-to-download will have much of an impact until 2012.
• Possibility of using these towards reoccuring expenses within HOME, such as club monthly fees.
• HOME could eventually create special items that could only be purchased with these discounts to give trophy earners something special that purchasers couldn't get.

Cons:

• SONY trades a slight bit of profit for potentially more customers
• More Hackers looking to exploit trophies
• More Developers making games with "easy to get trophies"
• May not be able to use credits on the things you most want to use them on
• If it doesn't work to encourage more sales backlash could be nasty.

Why this is necessary:

In most MMOs of this scale, there are attributes, activities, and gameplay that force players to replace their old stuff with new. In real life, things degrade over time or get ruined. In HOME, there is nothing but fanaticism to drive these purchases and this alone runs contrary to the interests of any of SONY's partners - because it takes away from what those fans would spend on DLC and other items already sold without SONY.

If gamers are able to earn money for HOME through playing games.  Then they will participate and some of them may even invest some of their real world cash into it afterwards since they have now invested time and energy into whatever they bought with the discounts.  And that's the key.  We don't want a skewed economy we're some of the users pay for everyone.  We will have a much more stable community and place to game online if everyone is able to contribute in their own way - whether that's paying outright for HOME items or indirectly by being a purchaser of PSN items.

I am still looking for feedback on this so feel free to chime in with your concerns, comments, and thoughts.  

I found some sources for the costs of a $60 game if you question my numbers (Forbes.com - Why Gears of War Costs $60 ).