hey Dave!
its tough...I was in the same situation early 2009.
I wanted something quicker, and somehow cheaper! but more track suited.
I looked at my current 33 - 255rwkw, same suspension, little bits here and there. and to make it go quicker - I needed to sort the suspension out for something better and bigger brakes - and tracking it more meant more chance of a rebuild and roll cage
that was about 15k as you said~! I had already poured alot of $$ into it so I cut my losses and decided to sell and now have a fairly competitive mx5 track car!
so yeah, dont know if im helping but if you buy the 33 GTR - what sort of coin would you put into it to go fatser than current 33 gtst? i wouldnt be too much however then the cost of maint of a gtr?
perhaps it is time to move on mate! you were telling me this at wakie earlier in the year!
10 years has been a good labour of love - time to move on!
OR...do what Ryan did!!