One thing in Costco's favor, they have just about the lowest prices around on tires and they offer free lifetime rotation, balance, road hazzard warranty, patches, nitrogen fill up and don't forget the green valve stem caps. We have bought a few sets from them and have been very happy with their service.
I have an '01 F150 with 58,000 miles still with the original set of tires and it looks like I can squeeze some more miles out of them too, always filled with compressed air. Makes me wonder if a Goodyear Wrangler would fit on the rear of the Rocket.
I have probably changed out over 10,000 tires over the years and have never seen the inside if a tire rot due to anything. In fact, even very old tires look brand new on the inside. Some tires, that have been run under inflated, tend to sluff off rubber on the inside and that will sometimes roll up into little rubber balls. I've seen tires loaded with very corrosive "Fix a Flat" but once you clean that out, still look brand new.
Its a snake oil gimmic.... and it works doesn't it
I've changed about that number too, Tom, with the same results! I've seen the occasional tire half-filled with water, 'cause wherever they got their air from didn't have a line-dryer and didn't drain the condensation out of their compressor regularly, but that's about it!
And one with a 1/2" x 5" wood lag bolt in it...
And that's the best point anyone could have made: Racing or really long-lived tires (industrial equipment, for instance) aside, one would never see the benefits of using nitrogen; the tire would wear out long before you could.
Stick with compressed air (preferably from a source that regularly services their compressor) and save your money for making that Rocket faster! Or prettier. Or both.