The two hacks I've released aren't big and complex... but they are nice and useful, and in the case of the Points system, appearently in high demand.
The only large hacks I've written are heavily slanted for my own forum exclusively and a lot of stuff is hardcoded into it that wouldn't port over.
I'd want a few bucks if someone wanted me to rewrite my Store for their forum... it would take days to do and I'm a poor stay-at-home father.
I've gotten several hacks off of here... and by writing a few and releasing them for free... I feel I'm paying the community back in a way.
As well, I'm not only having fun, I'm learning. Which is payment enough.