@mijael: you certainly raise some valid arguments, but I think that it does have 2 things going for it that will buoy the price and continue "some" growth:
1. The possibility of a Netflix series and/or appearance. (I know it's pure speculation).
2. There is among comic book collectors (as you stated) a fundamental appreciation for the character. (This factor is more of a contributor to its growth, especially as SA books in high grade are pricing beyond the reach of most collectors. Additionally, this book is coming of age in terms of seeing demand among younger collectors who have fond memories of MK). Will it ever rival the big names? No, but it doesn't necessarily have to in order to appreciate in value.