Actually I can understand your predicament since I asked my insurance company (Adrian Flux) and they would charge me £1000 per year LESS if I converted my 1.6 than if I went out and bought a Cupra (group 18). It would only cost me an additional £300 per year to put a 1.8T in the S but a cupra would be £1350 extra per year.
Leon S = group 6
Leon Cupra = group 18
Its tempting, but after brakes, suspension, gearbox, electrics and all that you end up with a car that is hard to sell, VIN nos dont match and it will cost you £4000 at least. Not to mention all of the electrical goodies that come with a Cupra like climate control and lekky windaz in the back etc.
I must say that the replies to your post are mostly right, you are better off waiting for your insurance to drop and then buying a cupra...