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. It doesn't have the cachet (appeal to collectors) of an original, so demand isn't there, and since it's not a limited edition, there is plenty of supply.
If you're buying already expensive records--original issue Rammsteins for instance--the supply is limited, but you're betting on demand staying strong. The current price is probably driven by hardcore Rammstein fans. Will there be more or less of those in 20 years? It's also worth noting that Rammstein debuted in the CD era, so relatively few of their fans are likely to have sustained nostalgia for the vinyl experience (nor were their recordings likely optimized for vinyl).
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.