Depends on how you define value. The funniest posts tend to be ACs. Ignoring anonymous posts also means you miss the ones that do have value.
I'm not sure that the ratio is massively different anyway, after all 90% of everything is crap (so we are only at a 10% difference at best anyway). I do agree that the worst posts are almost invariably anonymous, but I'm not sure that losing those makes up for losing the valuable anonymous posts.
This has gotten me thinking about when I click the anonymous checkbox. Usually when I want to tell an off-color joke. And I'm tremendously tempted to do it now just for the effect, but I won't.