The thing is i know its because youre getting 17s but i think springs would have a detremental effect unless you invested in some proper coilovers. Having driven the Cup on track its actually very good suspension wise. The brakes stood up well but im yet to experience a standard car which can cope that well. If i was in your position id keep the 16s and spend some money on the engine and maybe get some different brake pads/discs.
If youre that keen remember you have a true performance car, not a little supermini like me! Phone up the major companies and ask them if they have springs and dampers to suit your car, and ask them about them, have they any articles/reviews? Ask why you should be buying them etc. Too many people buy new springs and because its a slightly tidier handling car presume its much much better, youre always going to give the thumbs up to something youve bought after all. Do some comparative research!
-Rob