They do come up for sale and TBH the older ones are unpredictable, sometimes they sell for a fair bit of wonga, sometimes no more than a later one.

IMHO they are not really worth any major premium, I have both and the differences are relatively minor, both are built in the same way and you really need to know what you are looking for to tell them apart. Don't believe any misguided hype about "90% real firearm parts" and the like, sure, the slide and frame are steel, hey wow, () but you may as well start with an ingot to turn one into a 9 mil, not that that would be your intention but saying so just so you get the picture. Older and newer are practically identical, and also forget any "older machined steel, newer cast metal" - all parts just as with proper firearms are always initially cast to basic shape, then finished (machined) to size.

The innards are pure CO2 pistol but certainly much more solid than any monkey metal Umarex.

The barrels - certainly in the UK - are also always rifled, at least, although some advertisers make a song and dance about this latter, again I have never encountered one that had a smoothbore.

I would still pay "regular" money for an older one or just buy a later one, you wont be missing much at all, these are just plinker guns anyway.