As always it's supply vs. demand. I am building Exo, it is a killer set, a lot of fun, and truly unique. Simply stated- it's over-saturated, overly available, and heavily stocked by investors. Thus, it will not "pop" at the rate others will.
Regardless of the the theme, if there's more fans of a set than volume of investors hoarding, it's post-production increase will spike much faster. The show, concept, you name it doesn't matter. Limited interest from the investment community ulimately will make a retired set much sexier on the back end.
As Warren B. states, "when others are running away from an investment, run towards it".