Speaking for myself here only:
Purely a cosmetic thing, my car isn't quick around corners or in a straight line at that.
My factory 14s did not do do any justice to the lines of the SW20

17's look good. I still have my 15's, but haven't used them. Should really put some sticky tyres on them and use them a bit.

Flyboy

Why are you guys changing wheel diameters?
Doesn't it upset the handling?
They did spend millions on the setup research for the car after all....

Probably mainly for looks but also there is a much larger choice of modern performance tyres for the larger diam wheels. But being lower profile, they do ride harder.
 
Btw, the special 14 and 15 inch Yokahama tyres they originally designed the car to use, have not been available for years. 

Work Meister S1 2PC
Front: 17x8 +35 215/40/17
Rear: 17x9 +35 235/40/17
Suspension: Stock
 

I've gotta get some of those Meister S1s

Thread revival, has anyone fitted 10 inch wide rears with 285s? I currently have 9s with 255s and am thinking of seeing how far I can push it. (I also like fat tyres). I seem to remember there was quite a bit of space at the back still, but was wondering if anyone has gone that wide before and the offset required, currently I'm thinking +35 might be the best bet.

I'm going to be trying 275s with a 10" in about 1-2 weeks time, i'll let you know how that goes!

Yep, that would be awesome, thanks Dylan. I was thinking 275 range of tyres, but 285s have a much larger range of options that I can see from a brief look, which was why I was thinking that. Which brand of tyres would you be using for that?

I think its a hankook. I'll probably end up just running a 265 federal RSR however.
 
The extra 10-20mm with that kinda tread won't make a differences on the street for me.

Lumix: Do you happen to have a side on view with those wheels on your car.
 
Tossing up ditching the back 18s (double stagger) and keep in 17s all round.