The thing I can't understand is why people go up to 18" and use the 'wrong' size tyres... (looks mainly I guess)

In an ideal world, I'd have kept the std alloys, but no decent brakes available at the time. Didn't go to 18" because I wanted to keep as near to the correct rolling radius. When going up a size in diameter, you're meant to go down a profile and increase width. Follow that on an 18" wheel, and things get a bit more complicated....

Car handles and rides better on the smaller wheel imo, and brakes are 355mm with 6 pots, so reasonably big.

Function over form in my case.