This shows the new features in more detail, and now makes my list of parts clearer:
http://www.teamxray.com/xb4/
for upgraders, looks like the new wishbones front and rear, and optional (to 2014 kit) parts, like the new rear suspension hangers for low traction, optional brass rear weights, and maybe the new slipper bits (I had no issue with the old one?). The split chassis mod, I've done that already for the ralls racing under gearbox weight. no need to buy a new piece for that, only other difference is two holes for mounting rear weights. A drill and counter-sink can sort that ;-)
It doesn't look to me like a lot has changed, lots of the listed changes were v2 parts or running changes anyway, shock o-rings, bevel gears, v2 diff outdrives, etc.
Very interested to try the new 2mm offset wishbones for weight shift. also rear wishbones are redesigned to allow for front and rear shock mounting. I suspect this option will be a feature of the 2wd car.
I'll keep mine and buy a few upgraded bits.