I agree with you on the seats but I would only mod them after I destroyed them:
my list so far is custom cloth or fabric colors would be black and ice grey with red stiching
vinyl same color swath
leather if I had to same color swath.
Apart from that give me a good sound system a pair of shades and I am all set. Road noise or any such subjective things are kinda irrelevant to me, I prefer my car to be noisy and never had a car that didn't have creaks, squeaks, rattles, etc. I feel very disconnected when I drive a vehicle that is luxurious, hard for me to gauge the car. I have always loved my beaters far more that the cream of the crop cars plus when you mess up those luxury cars that really gets you mad as hell.
just my 2 cents
ps: prob not leather seats, i hate cleaning leather