That would have sucked for me big time as a kid. We constructed a lot of stuff that didn't exist as a toy out of styrofoam or cardboard and most of the time it didn't look as good as the toys - but we had an environment that would inspire our imaginations (we built the emperor's throne room for example). So I don't really envy the actors at all and I can imagine the difficulties.
Yet, in my opinion there's another thing that gets in the way of creative acting: The respect for something as big as StarWars. Back in ANH, no one knew or cared about what kind of weird nerd movie they were making, and thus dared to improvise a lot and all in all took the whole thing more lightly - the very thing that gave Lucas so much headaches.
I highly doubt any prequel actor dared to say "You may be able to write this stuff, George - but you sure as hell can't act on it.", like Harrison Ford did. Back then Lucas was forced to respect the actors' creativity and talent for improvisation.
Oh and gethedical, the best example of the hours and hours wasted in highly detailed cgi environments, is the "Order 66" scene. You see quite a few planets - and from the webdocumentaries I knew about the incredible amount of work and time that went into them - alas, you only see them for a few split seconds.
There wasn't enough time in ROTS to dwell long enough on important things and a lot of time was even wasted for stupid slapstick scenes - a thing no one did expect in "the darkest chapter of the saga".