I'm kinda ambivalent about this one.
I'm not sure this thread really represents a direct analogy to the Tex.SE "fun" threads.
My understanding is that the Tex.SE showcase threads are, in part, about teaching. Each of the answers is implicitly saying "Here is a cool trick I know," or "Let me teach you about writing elegant code." That makes them potentially relevant to many hardcore Tex users (not just the people literally doing scientific diagrams in Tex). It's notable that, as far as I know, nearly everything posted comes with source.
I think RPG.SE's character sheet thread doesn't really achieve the same goals as the Tex.SE show-off threads.
Is it relevant to the site's users? Doing your own character sheet layout isn't really a core part of playing an RPG. It's more of a graphic design activity associated with publishing one (or being a dedicated fan, sometimes). The vast majority of people involved in the hobby are never going to do this.
Is it relevant to the core mission of the site? I kinda suspect if you posted a detail-oriented question about how to make a character sheet (rather than an overview question like "What tools could I use?"), you'd be shunted off into Graphic Design or Tex or some other more technically-oriented part of SE.
Does it contain tricks you can pick up and apply to your own work? Probably yes, but not as directly as the Tex.SE questions do.
It's cool to show off and maybe this is good enough for a first-time experiment (one thing that makes it a great choice for a first-time experiment, despite my concerns about on-topic-ness, is that it's a pretty narrowly scoped question). But, well, what would more questions like these look like?
"Show off the games you've written?" (Seems like advertising.)
"Show off your actual play?" (But how do you turn that into a substantive teaching tool?)
"Show off your house rules?" (That'd be a disaster, I think. No focus. So many comment arguments.)
"Show off your character doodles?" (Is that in scope?)