That's interesting. Are you referring to MTBs specifically or vintage bikes in general? My impression over the last ten or fifteen years has been that there is more interest in vintage road bikes in the USA (and perhaps Japan) than in Europe. I think that the market for vintage MTBs in the USA has been pretty soft comparatively.
Vintage cannondale is hot in germany
Lot of followers and buyers there
In holland not so much. restored sells easy unrestored not.
Prices are about 50% here when i compare with ebay usa
I live near the german border so that helps a lot
Late 90,s is most popular
In the small collectors world Klein, GT and specialized are more valued