I don't think many people will complain if the aliens look a little different. TOS Klingons and TOS Movie Klingons got by just fine without anyone's head exploding. Similar arguments can be made for the Romulans, Borg and Trill who all underwent an image overhaul. We all know it's fiction at the end of the day. It would be nice if it was all set in the same universe so it all "matters" though. It was nice knowing TOS, TNG, DS9 and Voyager were part of the same continuity even if there was stuff that didn't mesh with previous continuity. I'd hate to see that shared universe replaced with the JJ Abrams one or a rebooted one entirely (though I could cope with a reboot if I had to).