The problem with the Wii U is that, not only does it have a very small library of decent games, but also that entire genres of games are simply missing from the system. When it comes to these genres, : shmups, fps, racing, action/arcade, and even RPGs, the Wii U doesn't even come close to the Dreamcast (or even the Saturn). I personally love games in those genres, and the Wii U just didn't offer them.
I will agree that older Nintendo games and systems (NES, SNES, N64) tend to appreciate better than most systems, but most of Nintendo's more modern systems haven't fared as well (GC, Wii, Wii U). The Wii itself is virtually worthless in terms of collectibility, and most of the games (with a few exceptions) are trash. The Wii U had a few gems, but not enough to make a difference in its ultimate fate.