I'm just writing to say how much I agree with your views on large wheels/low profile tyres. I recently sold my 1999 Lexus LS400 which had 15-inch wheels and 65 profile tyres. I now have a 2007 Lexus GS300SE which has 18-inch wheels and 45 profile tyres - the difference is quite noticeable. Whilst still a beautiful car to drive, the steering on the GS is more twitchy, especially when braking, needs more correction and is much less forgiving of road surface irregularities, ruts, etc. to the point where it can pull quite strongly on the steering wheel. In this respect, it's not actually as nice a car to drive as the LS.
There is also more road noise, plus I suspect the car won't be as good in cold, slippery conditions.

I've had the tracking checked and made sure the tyre pressures are correct, but all is well there, so I guess the above are "characteristics". Given all that first-hand comparative evidence, the only reason I can see for fitting huge wheels with ultra low-profile tyres is that they're ‘trendy’. Is there a more sensible wheel/tyre combination I could put on my car to improve things, possibly from an earlier GS or LS, bearing in mind it would have to have the same rolling circumference and clear the brakes? Looking at the latter, it looks like I might get away with 17-inch but possibly not 16-inch. Also, for my low mileage, can you recommend a good year-round tyre that will cope well in all conditions.