With the 08' Worlds around the corner you will see the K-Cars get a complete make over that is influenced by Gil Losi. You will also see the Mugen move to the 6 version. I would predict a little buyers remorse if you went either of those directions. With that said, The Mugen is a very good car right now. It is stable, will keep you out of trouble and is rock solid build wise.
I have never really cared much for the Kyosho but I think they will be the ones to watch in 08'.
The Losi will stay as is and you might see a few detail updates.
The Xray will certainly change a little. They always do as they search for every detail to make them the best in all conditions.
TEX