Aliens need be no problem in GTW if you don't want to use them. I deleted all the aliens in the Family bin, never had a Sims abducted (wouldn't have minded though), haven't been to Sixam either. They do tend to turn up in bars though. Just use the mods as above because GTW can be great to play.
But.....I have GTW and just ignored the aliens but now have downloaded those Sims 2 families from Strangetown (Nervous Subject etc.) after buying StrangerVille and both families are busy building their own spaceship to get away from Mother. They add a lot to the storyline of StrangerVille for me.