No. Other prologue titles generally looked the same as the eventual full releases. There will be tweaks and small stuff, and maybe even some stuff that's very different yet not clearly better.
The gap between a GT prologue and the full released is where the developers add more cars, add tracks, tweak physics, work on tuning effects, etc. The graphics engine is set and won't be significantly reworked. If they were going to do any real major upgrade in the graphics department, they'd be calling this title GT5 instead of GT5: Prologue.
As for GT6 making it onto PS3, I think so. There's certainly a chance it won't (Polyphony isn't the most timely developer), but there's a lot of time left in this generation, and they'll be able to use some GT5 assets as a base to shorten the development time(as has been the trend in making two games per system).







