You're seriously considering getting rid of your car because of the stiff ride? Did you test drive it when you bought it? I test drove one Sport (non-SAP), one Limited, and two Base models, and I could tell the difference when going over uneven surfaces.
KBB says the value is $26,748 +/- for excellent condition. And that's if you find a buyer (if I were in the market, I'd buy a new one at low APR for that price differential). So that's $4000 depreciation (plus sales tax and license fees), plus your payments. For 8 months of driving enjoyment. Now that's a very poor investment. You should just keep it. Deal with the ride for now, and switch to more comfortable non-runflat tires when the first set is worn.
Another option would be, in addition to switching out the tires, switch out the Sport suspension for the Base/Limited suspension. I don't know if it's 100% compabible, but it probably is. I'm sure it's cheaper than the loss on selling the vehicle and buying something else.