Mr Nelson, I'm just curious what tires you use for just for reference.
I was referring to the Vredestein Volante TriComp as my $40/3000-mile tire (actually, it's MSRP of $50 and often on sale for $30), and the Schwalbe Marathon XR (no longer made) as my $70/8000-mile tire.
I'd say that carrying a spare is unnecessary unless you will be touring somewhere really remote.
I did the entire TransAm starting out with relatively new Schwalbe Marathon XR tires, did not carry a spare, and had no problems (I didn't even have a single flat in 4600 miles). I started out the Northern Tier with the same set of worn XR tires, this time I did carry a spare, and I needed it as both XRs failed along the way (as I expected them too). So I agree that if you start out with a new tire that will most likely go the distance you have in mind, you don't need to carry a spare. But I've read about enough problems due to bead separation or hitting a large piece of sharp metal that carrying a spare is not that bad of an idea anyway. I carried one spare and when I had to use that one, I had my spare spare at home mailed to me.
Most of the time, folding tires are only marginally more expensive than wire bead. The one (very misleading) exception is the Marathon Mondial (Schwalbe's replacement for the XR), in which the folding tire is twice the cost of the wire bead, but that's not because of the wire bead--it's because the folding version is a completely different tire than the wire bead version, sharing a name and nothing else.