Car appreciation... the aesthetics, the engineering, etc

A couple of years ago I'd have said no, as I assumed it was a covid fad. But I think they're solidly locked in as a status symbol now.

I think emissions will be the thing that kills a lot of them off.

Depends on the van massively. The right ones at the right money have never really done much depreciating. Stick to VW, Westfalia, Reimo, Danbury, Bilbo's etc. and you'll probably do alright. Ex-builders vans with big miles and homebrew conversions are best avoided. The more classic stuff has definitely taken a hit recently, but it can be hard to judge as condition varies a lot. They can also swallow money very easily in upkeep. I speak from experience...

A high spec Highline T6/T6.1 will hold value well (everything T6 onwards is Euro 6 ULEZ compliant). DSG probably better than manual.
IMO a normal Kombi layout with 2 captains seats up front and rear bench seat will retain value better than a camper as it will have a much broader market when selling, but if you specifically want a camper for actually sleeping in regularly this is a moot point.

Anything T5.1 and older will not be ULEZ compliant.

Read up on T28, T30, and T32 variants. Some people will avoid T32’s as the 3200kg max load weight rating brings with it more expensive parts to deal with load rating, (I recently fitted Twin Mono Projekt coilovers on my T32 and it was ~£400 more expensive than theT28/T30 kit). In some cases a T32 will require a type 7 MOT, although if a camper or a Kombi it should only need a type 4 MOT, as Type 7 should only be for panel vans with max laden weight of over 3000kg, but some MOT testers are not aware of this. A type 7 MOT will check things like if load rating of wheels and tyres are up to spec etc.

Do we think that VW camper (and analogues)

Aren't you going to tell us what you're mulling over?