This is in relation to a conversation with @adam on IRC, but I forgot to file this in the forum until now 
As far as I know, as of this writing, advanced variables only work in the default post template and nowhere else. So I hope there will support for more flexible variables / metadata / tags for other templates in the future.
What I was trying to do was create a summary variable to store a brief blurb about my blog posts (basically a TL;DR), then show those summaries on my blog landing page instead of the default preview snippets.