The difficult thing about the Snacktime Kids is that they're somewhat hard to find a buyer for since you can't sell them on eBay with them being a recalled item. And also, they need their backpack in order to work, and many times they're missing it.
I don't know enough about head molds to help you out much there, but there are different countries/factories of origin for CPKs (noted on their tush tag), and some of those are more sought after. You want to look for CPKs that are made in Spain (Jesmar), South Africa (Triang Pedigree), Japan (Tsukuda), and Mexico (Lili Ledy). So definitely check their tush tags to see where they were made; I think the dolls may also be marked with the info on the back of their head (or at least my Jesmar is stamped that it's "manufactured by Jesmar, Made in Spain" on the back of her head, but I can't speak for the others since I've never owned any of them).
Hmm, I can't really come up with anything further as far as hard-to-find goes, except the previously mentioned "Little People" soft sculpture CPKs. I recall that the slightly smaller 'bean bottom' CPKs, in nice condition (since they're prone to 'pox' on their head), used to have a bit of a following, but I'm not sure if that's the case anymore. Also, of the newer CPKs, some of the Toys 'R Us (TRU) brand ones are desirable and have a little bit of value since they don't make them anymore, plus they were somewhat limited to begin with. TRU Cabbage Patch Kids are a little bigger than the other brand of modern CPKs (Playalong), and they have a slightly different look to them. Their tush tag, as well as the back of their head, will note that they are a TRU Edition.
