I think one of the things that may be happening recently is that the almost absurdly high prices being paid for some of the more popular "collectable" Spydercos is causing more people to look toward some of the models where there is (or at least was) less collector interest.
As for the knives themselves, both are interesting concepts, and work better than the pocket clip under certain circumstances. The Snap-It is, unfortunately for me, strictly a right-handed knife. When closed, the snap totally blocks access to the thumb hole for left handers.
The Remote Release is more "universal". As Shmackey pointed out, a new version of it is due out next year.
You have to take the term "rare" with a grain (or ten) of salt when you see it on eBay. Have seen current production models readily available from hundreds of sources described as "rare" there.