If you already have the GK (or equiv.) pickup system then yes, the V-bass is worth $300. The newly announced VB-99 will list probably around $1300 to $1400 - street will probably be $1100 +/-.
I have a V-bass and it does synth sounds very well. It doesn't do piano sounds though...unless you program it and then it would not be that good. Brass, organ - those are pretty good. The modeling - well, I'm not really a modeling fan of any of the gear out there - but you do have a lot of sound sculpting options. The polyphonic octave capability is really cool - and if you factor just that and the 'regular' stomp box effects it has, then $300 isn't a bad deal.
Tracking is pretty good, in my opinion though you can still get glitching on some of the mono pitch shifting effects. It doesn't output midi-note information - just control info like program change, etc..
Hope that helps... If you have any more questions about it - let me know!
Dave