This has happened with Star Wars in past years.
While the value of "SOME" vintage vehicles may drop in price, it's not purely due to the new ones coming out. Most collectors of GI Joe have been doing it for years now, and have the majority of the original vintage vehicles coming out in the 25th line.
The demand for vintage items has dropped from any line that has had a relaunch (Star Wars, GI Joe, He-Man, etc).
So while some people can't see the point in paying more for a vintage item, I 100% can. The new stuff might be more durable - but I'm not playing with them, so what do I care?
The new stuff may have a fancy box - but it's not the vintage box that I remember.
As I've said before, I love the 25th line, and think Hasbro did an amazing job with it. But nothing can replace the original items, or the memories I have associated with them.