The 172 is a great car - I love the leather, and the xenons, the ABS would be useful if I ever find myself in an emergency situation in the wet, and Air con would be great on those hot summers days.......
But for me the Cup has more road presence (due to colour, it looks more chunky - due to the different wheels, wider / lower stance), is more focused, and id rather forgo those extras and enjoy The car in its more raw form. The performance (as in speed, there isnt a great deal between them, but handling and feel.....there certainly is, fact.)
Each to their own, if you really want to change, do it!! Just make sure you extensively test it - rev the nuts off it / chuck it about for quite a few miles on different roads without the salesman in the car!! (Didnt you do this prior to buying one - if im gonna spend 13K on a car I want to know ive made the best possible choice in terms of what I expect from a car ive got to keep for 2 or 3 years!!! But then again, if you dont drive it in that way normally then you wont appreciate the difference anyway......but why choose the Cup to start with? It cant be price surely cause if youre gonna spend 13 you may as well spend 14,500 and increase your finance per month by what......£40 ish over 3 years??