Yeah, it seemed that George always wanted to put more and more different races in the films, but he really wasn't able to manage it until ROTJ, which is when there was that explosion of goofy band puppets, Mon Calimari, and Ewoks. Obviously that sensibility continued into the prequels where, suddenly two out of three characters are non-human humanoids or non-human non-humanoids. Not that it's bad, but it certainly does disconnect the universes, although I'm pretty sure it's been retconned away as aliens being subjugated by the Empire. In fact, the X-Wing novels, I thought, did a good job of dealing with that plot point when those damned asshole bothans attack the New Republic for being racist and point out that aliens were only used in the rebellion towards the end.