It seems to me that, much like the OOT, the episodes of the saga should all be snapshots of a much bigger story. The opening crawl gets us up to speed with where we are in the overall story and everything else is picked up from the characters as we go. I feel that the expository dialogue in the PT was clumsy and unnatural, something that, for example, Ben's dialogue with Luke in Ben's hut on Tatooine, does not suffer from.
Having a gap of 20 years between episodes 3 and 4 and episodes 6 and 7 and then 3 years between the others at least gives some basic structure to consider when 'mapping' the plot. This may not be exactly how it works out, but it is useful when working out ages of characters, how long things have taken, etc.