I agree, I don't think I'd decide to buy (or not buy) a car based on the sole reason of no spare tire.

That being said, I think the people who say the can of fix a flat and Road Side Assistance is all you need, have never used either. On day 3 of ownership of an M3 Roadster may years ago, I got a flat. Pulled out the fix a flat and really did nothing other than make a huge mess of the tire and wheel. My call to Road Side Assistance ended up in a pretty headed debate about the existance of a spare in Z3s. Non M Z3s had spares, M's did not. This point was completely lost on Road Side Assistance. Regardless, 4 hours later a tow truck arrived to take my car to the dealer for a new tire.