Good idea but I do see a few hurdles...
1. Passwords to all the commentators/reviewers?
2. Intentionally misleading "sound" advice or criticism - might be overshadowed by the quality advice but who can judge that one way or another... especially in a case where what works for one site would fail another.
3. Seems like weeding out the spammy dime a dozen generic crap would be a major headache
4. I know it would be an altruistic enterprise... but where is the money in that?
Goodwill? In this business? I think we are all conditioned to be too paranoid...