They still use polystyrene bricks today. And IIRC, the sets of VOY were made out of the same materials as the sets of TOS--namely wood and metallic paint.
IMO, there was a natural progression of things from TOS to VOY. Of course things in VOY were supposed to look more advanced than things from TOS. It wouldn't be right if TOS didn't look more primitive than VOY, really...
I dunno, it just seems like most of the complaints I hear about TOS from fans who were first exposed to the later shows seem to focus soley on how TOS looked rather than whether or not they simply didn't like the characters or the stories.
Free your mind, and the rest will follow.