As with anything else, price is a function of supply and demand, and collector's markets are notoriously subject to trends and bubbles. In terms of vinyl, collectors are usually interested in original issues, although sometimes there will be a limited edition reissue especially designed to appeal to collectors.  A mass-market reissue of a classic band is unlikely to ever be worth much more than the cover price.

If you're buying already expensive records--original issue Rammsteins for instance--you're betting not just on supply, but also on demand. The current price is probably driven by hardcore Rammstein fans. Will there be more or less of those in 20 years?

In short, I would say this is a terrible investment strategy. If you enjoy the music, buy it and listen to it. If you don't, don't. In 20 years it's just as likely to be completely worthless as extremely valuable, and if you're keeping it in the cellar all that time, it might not be in good condition by the time you dig it up, anyway.