I use non run-flats for my winter setup. The ride is noticeably better than the standard issue summer rft's that came along with the car...
I am not sure about this... but a friend I know also runs a slightly under-inflated setup for a softer ride... i.e. about 2 psi less than recommended. Of course, this could result in uneven tire wear, and more heat buildup... but if I were to venture a guess, a couple of psi's should be OK.
As far as selling the car... I explored that (for other reasons)... and you could lose a lot vs. trying out these options.