P Zeros are shocking tyres. You may not want MPSS, but in stock sizes they're close enough in price. I'd actually rate the 453 as significantly better than P Zeros, and by some margin.
Also, if you're willing to shell out for new wheels then an extra £200 on decent tyres that will last you so much longer than anything else, you're actually saving money!
For me, the biggest downside to bigger wheels is the weight. Unless you spend £££ on ultra light wheels, then you're adding weight to the worst possible place on the car which will make you accelerate slower, increase braking distances, and affect the turn-in for the worse. You'd be better off lowering it and changing the colour of the wheels if you want it to look better.