I guess I'm looking at it differently.
In the prequels, there was supposed to be, what, 1000 years of prosperity and peace or some such? So sure, they got to the point where aesthetics played a huge part of vehicle design. We started to see a slide into utilitarian by the end of the prequels and it was full on in effect by the OT. The Empire was spending money on quantity and size over appearances, meanwhile the Rebels were making the best they could out of whatever.
Keep in mind, in the span of about 18 years (Revenge of the Sith to New Hope) you had an entire Republic fall and replaced by the Empire. The OT only takes place over the span of a few years at best. And now the new films are 30 years later. So 50 years to see one 1000 year old galactic government fall, be replaced, THAT government fall, and now attempt to replace itself?
I think I'm ok with not a whole lot of innovative ship design. In fact, it would seem strange to me if things WERE radically different. I'd be asking myself how the scattered Empire managed to pull that off.