That might be the case for a few individuals but is surely illogical when applied to the market. With respect, you are putting the cart before the chicken.
If used Cali values are relatively high (compared to say a £70k BMW of the same vintage) that's because there's a high demand for used Calis (compared to used BMWs).
If a lot of individuals started buying new just because a used van was nearly the same price, then demand for used vans would fall and prices for them would fall.
Supply and demand, innit.
The reason expensive campervans hold their value better than expensive BMWs is (presumably) because the utility of a 10 year old camper is pretty similar to a new one, ie you can camp in it. While the 'utility' of a 10 yo Beemer (which when new was largely about pub bragging rights, TBH) is drastically impaired by the fact that the acne-disfigured trainee bookmaker* down the road now has one just like it, with bolted on stainless steel wheel arches.
I'd say that the Cali thing must also to some extent be something to do with an artificial constraint in the supply of new Calis (Hannover production limits, and the emissions fixes) that is driving the value of used ones, because a lot of folks don't want to wait 6+ months to get hold of a factory fresh one. A good game for a manufacturer in the short term, but risky in the longer term.
(* With apologies to the Turf Accountancy profession).