Welcome, moviegoer...it's nice to meet you. I hope you come to love BetterMost as much as me...there are lots of fine people here to get to know who share your obsession, sure 'nough.
For me, I haven't yet crossed the threshold of 'thinkin too much' about Brokeback Mountain, so I guess you have to be your own personal judge of that. Of course, I don't want the movie to 'quit me' because it's inspired me in so many ways.
I like your parallel thinking about Jack's closet with the two bloody shirts, contraposed with Ennis' hidden shrine at the end of the movie. It probably is the most 'obvious' metaphor for the general viewer and it works at that level, without a doubt.
I like to remember though, that Jack's closet space was open for Ennis to see into. I'll argue to the death
that Jack's Mom knows of the shirts being there and fully understands their importance to her beloved son. And that is contrasted with Ennis' closet, because he closes the door. Of course, the open window leaves us with hope again. I'm sure others have thought about this in more depth than I could possibly do justice.
The point is that you're not alone on fixating on symbolism like this.
Again, welcome!
Lynne