I’m a big fan of Should I Work For Free? - my personal three-tier approach to anything I write is a little more basic. The following works for me, but I guess it can be applied to any creative endeavour.
If it doesn't pay much (if anything), that’s OK...as long as you are having fun.
If it doesn't pay and you aren't enjoying it, then that’s OK too...as long as you are trying something out, teaching yourself how to do something, testing yourself or experimenting in some way.
If it doesn't pay, isn't fun and you aren't learning anything...then you really have to seriously question why the hell you’re bothering with it at all.
All of which can be distilled down to my overriding mantra:
"If you don't take money, they can't tell you what to do." -- Bill Cunningham
“Art is long and life is short, and success is very far off.” -- Joseph Conrad