I'm generally just relieved that the back door is still there and not lost to wherever they all seem to go.

I think this is a natural thing to want to do when you get your first pinball. You're excited and want to fix it up. Certainly nothing wrong with detailing the back door but most eventually learn your efforts are better spent focused on other areas. Like the dummy reel as mentioned. It does look like a nice clean example. Probably doesn't need too much but you can always find little things to improve upon if you want to.