Kris, I never see the price of Iltis skyrocketting as you say...
Yes there are fewer of them around than the comparative M38A1 series jeeps.
Another point is that an Iltis is not a Jeep, nor should it be referred to as one. Collectors should be knowledgeable enough to realize a difference from the ideology of the general public and their perception that every small 4 wheeled mv is a Jeep...
Another thing that I must point out is this; rarity does not equal value in all cases. While rarity does factor into the value equation, collectability and condition actually plays a bigger part.
If I may illustrate this with an example;
An old baseball card that is very rare because the player was a no-name who never went anywhere in the League and is in tattered and torn condition is almost worthless. Why?
1) who was this guy and what did he do?
2) does anyone care?
3) how many were made?
4) the condition is terrible
5) has a price precident been set on like examples?
I would consider the old AMC Pacer to be relatively "rare" as well but don't see too many around, let alone be highly sought after by car collectors either...