I'm not an expert but an RGV is like any other bike, it needs looking after.
A good one will be fine but you need to get a good one.
Why worry about it being an ex race bike if you want it for track use? An ex race bike is the best way to get one which is fully sorted and is hence less likely to go pop.
The RS Aprilia uses the same engine and costs more, GSXR and FZR 400's are every bit as unreliable as an RGV, CBR is SLOW but handles beaytifully, VFR is a little quicker but not as easy to ride, RVF is no quicker than a VFR, it's heavier and way more expensive and the ZXR is the racers choice, also the fastest.
I see no good reason to buy a 400 over a 250 stroker but bear in mind that a 250 takes a real good rider to get the best from it, and you will have to be prepared to look after it properly.
Check out
www.rgv250.co.uk and
www.400.greybike.co.uk for all the good advice you could possibly want.
HTH,
Jen.
[Edited on 6-2-2006 by desmojen]