I'm all for innovation. I love seeing develeopers try new things even if it doesn't always work. But I believe this idea is far too open for abuse. If they do a voting system where players thumbs-up or thumbs-down people they play with, it won't work. Friends will vote each other up, people will vote others down just to troll, people will spam forums/games asking for votes up etc.
If Valvue chooses people specifically and marks them as 'nice' players or whatever, it would pretty much be restricted to competitive players, or people who contribute a lot of things to somehow get their name noticed. meaning a majority of the community would be unnaffected and still paying full price. I guess it might encourage the community to do more :S but they already give people like that small rewards don't they?
I read a comment above about charging people full price for the games, but rewarding players with 'points' that are redeemable for things in on Steam (At least I think that's what it was, I may have misinterperated it) Which i think sounds like a better idea.
tl;dr: Theoretically it's an interesting concept. Practially it's too open to abuse.