I think, in cases like this, it depends on the series. There are certain series that have elements that I would prefer remain shrouded in mystery forever. In Star Wars case... it's become such a massive series, and I'd argue a large portion of the most appealing mythos were shot point blank by the prequel trilogy. I mean, the only real mysteries I can think of that we have left is the origin of the Jedi (which is now being unveiled, though frankly, it's not something I feel demands to be left to the imagination) and Yoda's backstory. There are lots of other little details that we don't know much about, but those are the two big ones I can think of. We've known about the origins of the Sith for ages, if it means anything. There is a certain inherent appeal in leaving the Jedi's origins a mystery, though if it comes down to a choice between upholding that continuing mystery or a good story (which, so far, DOTJ is proving to be), I would prefer the good story.