What was up with the BROKEN WINDOW?!

I believe both times they focused on the window, Gabe was mentioned. Didn't Gabe use to live with them? Maybe that's the room that he lived in. Aside from the broken window, the only other thing I have a question was, when they did the Montage near the end, they showed a room full of old trumpets. Was this maybe the same room where Gabe used to live? Or was this the room in Miss Pearl's house?

I had the exact same question.

Just a guess... was the unfixed window a metaphor of Troy's neglected home life?

Troy fancied himself such a good provider for his family but he neglected a lot of things, too. It showed that he was more talk than walk.

For example, he lectured his son about having the foresight to fix the roof while not even bothering to fix the window.

I think it was Troy remembering how close he was/is from being a destitute wreck. He talks of how he has to work hard to keep his home (and life) in shape, to keep the rain from pouring in through an old roof. But right next door is a blighted, abandoned home with broken windows. The times when he looked at it were times when he was really down and thinking about losing everything.

"Smokey, this is not 'Nam, this is bowling. There are rules. "
-Walter Sobchak