All of the above?
Except: I suppose it could be argued I don't really do it to
save money, otherwise I wouldn't have 4 eco-cars. But not spending a pile of $$$ on fuel is definitely a big factor.
I do it because the subject matter is inherently interesting. And it's fun pushing the envelope - a personal challenge & educational too.
EDIT: PS rusty memory bank is suggesting this discussion may have taken place in an older thread. No big deal, though - bunch of new people around since that happened.