I'm driving my second S70 and can relate with your frustration. The S70 rides like an empty dump truck, although it's slightly better than the '94 850 I had. Here in NE Ohio the roads can be rough and I find myself pre-thinking my route in order to choose the smoothest one. That's a terrible testimony to Volvo engineering but, otherwise, I love that car.

I have found that 30psi in the front and 27psi in the rear give about the best ride I can expect and I'm usually alone in my car also. With the alignment in good shape and regular rotation, I still get over 40k miles from a set of tires. I'm aware that it compromises gas mileage a bit but, according to my computer, not very much and I consider the ride benefit to be worth it.