But which is worse: wasting a few hours of your life on books you didn't like, or wasting even more hours regretting the waste, posting to F_S about it, and then wasting even more time discussing how much you regret the time wasted?

Those hours are gone. Regret won't bring them back. Talking about your regret won't bring them back. When you go on about how much something was a waste of your time, you're only wasting more time on that thing.

Look, I've been there. I understand. But the only way to redeem that "wasted" time is to move forward, get involved with something you love, and decide not to waste more time on things you don't care for in the future.