I agree, so do I. I've followed quite a few cases here now and have yet to see one where reward money helped, even when the reward was a significant amount. Obviously there might be some that I've missed, but so far in the cases I've followed it hasn't seemed to make any difference in finding a missing person, or in finding their killer.
One case I'm thinking of in particular is Elizabeth Collins and Lyric Cook, the cousins in Waterloo. From the sounds of things there are all kinds of shady people in and around their lives who you'd think would be pretty tempted to snitch, given the high reward, but as far as we've heard there's nothing. (granted, something could be going on behind the scenes that hasn't been reported)
I think if someone's a good, moral person and knows something, they'll do the right thing... and if they're not, I don't know that reward money helps that much. That said, I do think it gives the family something to focus on and feel like they're helping the investigation when they're probably feeling pretty helpless. And like I said, maybe it does work sometimes and it just didn't happen to help in the cases I've followed.