From what I recall, they actually DID build the Jedi Temple floor as part of the set, but after cutting the film together, decided they weren't happy with how it looked, and since the sets had been struck, the actors all gone off to other projects, it was cheaper to build a digital replacement. Much like ILM often replaced sets and backgrounds with matte paintings (have a look at ILM:The Art of Special Effects, if you can still find a copy....great prints of most of their matte work!). The idea of replacing or adding to what you shoot, building half sets, isn't new.

"Watto, Jar Jar, Dex, Boss Nass....even though they aren't human you just cant recreate the realism of some of their movements or facial expressions..."

But my point is that you don't get even that close with rubber masks. The OTHER "Why Bother" reason is the same reason effect have been used and have continued to evolve since the beginning of the century...because use pushes development, refines and improves the art. Every time you do a shot, you learn something you can use on the NEXT shot. Pure R&D certainly plays a part, but actual practical application of what you learn in R&D drives the artform forward.

Anyways, at least I think we CAN all agree that Lucas needs 1) a writer 2) an executive producer who's not affraid to say "NO George".