I have a 2007 SC430 and changed from Bridgestone Blizzak run flats (installed last winter) to Bridgestone Potenza RE960 AS Pole Position tires four weeks ago: I am absolutely delighted with the change. The car now feels like a luxury sports car and I don't have to apologize when going over a bump in the road or hitting the edge of a pothole. The new tires also handle extremely well on the expressway. You'll probably do well with several other top brand tire names, however the Bridestone Potenza RE960 AS Pole Position tires are top rated by consumers at the Tire Rack online site. Bottom line, there is a definite and noticeable improvement in moving from run flats to aerated tires.
As background, I switched from the original manufacturer run flats to the Bridestone Blizzak run flats this past winter. I waited until the Spring to order the Potenza RE960 AS Pole Positions from Online Tires.com and then had my local Lexus dealer install them. I had them mounted on new rims so I could quickly and easily switch tires next winter. The dealers charged extra for installation of the air pressure sensors.
Re the spare tire question, I did not get a spare tire (Lexus wanted a fortune to convert over to their non run flat kit) and instead purchased a bottle of Slime and a portable air compressor and placed that in the bottom half slot designed for the spare tire.
