I support project $10, partly because I follow the reasoning behind it and sympathise with the developers and publishers, and partly because it shouldn't affect the people who purchase said games at all.
First you have to assume that the model for selling games is changing - no longer do you pay $60 for a game. You now pay $50 for the game, a transferable product, and $10 for a one-off non-transferable licence for extra DLC/multiplayer/whatever is the flavour of the month. As someone who buys and plays new games it doesn't matter, either way you pay a total of $60 for the complete package.
Things start changing when you go to sell the game. Before you were selling something with a base cost of $60. Now you only have something worth $50. Obviously this means the trade in value is less than it used to be, and by extension the cost of used games should also go down, so that the value in buying used games reflects the fact that you need to pay an additional $10 to match the content in a used game.
This just means that consumers need to be informed when they make used purchases, so that the price they pay is suitable whether or not they have to pay for extra content.
This model will be strongly affected by how Gamestop and other used games dealers respond to Project $10. I confess that I don't often buy used games anymore, so I don't have any experience with how such second hand games are priced. Also, the above model would make selling games a less enticing proposition, and certainly a less fruitful one. The trend of people who buy new and sell games to fund their purchases will be affected if they start to get less for their old games.
Personally, I find the best thing is to wait and buy new when games are cheaper. I'm lucky in this way because I don't much care for multiplayer so buying early isn't as important for me. Coincidentally this means that Project $10 isn't really an issue, which may be another reason why I don't mind it. As an example, only today I saw BlOps and Ass:Bro for £25 each, brand new. If I wasn't being particularly frugal (you might say stingy) at the moment I would have bought them then and there. As it is, not only do I have a huge back catalogue of games, so I try to force myself not to buy more, but also I know that if I wait longer the price will only continue to fall (although actually for these two games it may take a very long time - I waited until 2010 to buy COD4 because it kept its value so well and I couldn't justify spending a lot of money on such an old game).