Well, even if I agree with you in the fact that there's something different between PT and OT troopers, I think it is more a difference in the way they're filmed than in their suits. In the OT stormtroopers are more a background element than characters while in the PT they have their closeups.

And I think that if you look carefully at the photo Jaitea posted, well, there you have an actual prop which still looks like CG. I've been thinking why does that sensation come to my mind and I realised that while OT armours are shiny, PT are dull (I think this could have been done to save rendering time by not havin all those reflections). It'd be interesting if somebody that masters photoshop could trick some picture to see how would a shiny clonetrooper and a dull stormtrooper look