Hmm, I think that I would buy a V.5 because I read in one topic that the V5 isn't coming anytime soon. So if I were you I would buy one to experience new characters, jobs, and features.
I ahd the smae problem myself! I couldn;t decide if I should get a 4.5, because I already had a v4. Well I got together some loose money and decided to get a 4.5 anyways. I love the 4.5 so much more than the v4 now! The games are amazing, and the characters are new and unique. I say that if you have some money, get the 4.5! It is so fun!
P.S. The purple Lava shell is really cool because the background is a little city!