Square let us redo quests on different classes.

[Vele]

I think I'd like redoing sidequests for all the dialogue I missed out on, when 3.0 dropped I was pressured into hitting 60 as fast as possible for my static so I skipped a lot...
...
but then I think of those moogles in Churning Mists...

Thinking about it I guess it depends on how it's approached. If you can select any sidequest to repeat as many times as you want and still get full exp from it every time, it could possibly be abused... There's a handful of "talk to this guy that's not really that far away from me" quests, no?