As others have already pointed out. I think that some vintage cards are undervalued. If you ask me, they all are, but the market is somewhat different now.
A lot of new fans don´t have the nostalgia for WotC cards. If they see a POP 19 holo first edition PSA 10 Smeargle they don´t think, wow, what a gem. They (may) think, who is Smeargle? Umbreon and Charizard cards (for example), however, may very well start to shoot up again if the attention shifts just slightly.
In the end though, I would not buy a POP 15.000 card for 2k because I´m not sure if hype is a big factor in that price. I would take a look at the ´in between´ era´s, like Black & White and X & Y. These cards have PSA 10 POP´s of around 500 or lower and feature popular Pokémon often. They may well be set to rise.