I've got a 1967 Olds Cutlass convertible with frame rot but it does have factory AC and runs great. Since it has factory AC, how rare is this car?

 

It is probably more rare to not have AC than to have it.

 

Today, maybe, but not in 1967. In those days, A/C was still considered very much a luxury, even in high-end cars. It certainly was considered an extravagance in a convertible, especially in a more for-the-masses convertible like a Cutlass than, say, a 98 convertible. It wasn't until the 1980 model year that A/C became standard equipment on a 98.

I think the OP's car is rare in the context of how many '67 Cutlass convertibles were also ordered with air-conditioning, but there is no such thing as a "rare meter," so answering a question like "how rare is it" more precisely is pretty much impossible.

 

But trying to find one that was non air is lots harder today. Nearly all 66/67's today have factory air, far more than non air cars.

 

I think it also depends a lot on geographic location. Non-AC cars may have been prevalent in cooler climates, but growing up on the Gulf Coast just about every person I knew with a car newer than the 50s had AC. It was essentially standard equipment on new (70s - 80s) cars on the lots, labeled as a no-cost option. If a car didn't have AC, it wouldn't sell.