I had nitrgen put in both my BMW and RX7 when i got new tires. The guy at the tire shop told me it stops dry rot? I have since sold the RX7 and left the BMW to my sister since i moved for college. I had no problem out of them at all, and as far as topping off the tires, the BMW is still right at the orginal tire pressure.
just some additonal input!
KB