The only ones that I know of that actually go up in value are the ones that are discontinued. Let's say Balvenie discontinues the 21yr Portwood. I (and many others) would begin purchasing as many bottles as we could find and/or afford. If you happen to have a bottle you purchased last year for $160, it might be worth twice that in a few years (once the supply is completely gone).
However, that is a lucky projection, since there is no reason to believe the Balvenie will discontinue that expression.
On the other hand, we know very well that some bottlings are destined to be discontinued, as they are vintages (eg., Glenrothes), or independent bottlings. The tricky thing about these is that while they will be discontinued, they may not demand all that much once they are.
Good luck with your purchases! Please understand that you may be the one drinking them in 20 years, so buy the ones you enjoy!