So I guess your question is really should this be extended to more low-level offenses like minor traffic violations?
It's an interesting question. In Switzerland, for example, speeding above a certain level ceases to be a fixed fine and is instead a percentage of your income. I'm a fan of that. Fixed fines tend to discriminate against the poor disproportionately.
I can imagine there are many people who would be better off and would prefer 2-4 hours of community service over a $100 fine. So that should certainly be an option instead of paying the fine.
Yeah I think the idea probably does have merit.