Although Z2X and Z2-S are both discontinued, I am not aware that either model is particularly "collectible"
Although there are exceptions, most of the more collectible vintage SF items were from the modular era.
As to which had a larger production run between the Z2X and Z2-S, I don't know (although that information may possibly be available somewhere) ... but if I had to guess, I would think that "strobe" models generally seem less popular, and thus may be more difficult to find :shrug:
The closest thing I can think of which might be similar, and perhaps collectible, would be the AZ2.