I have setup a tent in the shelter before, at Baldpate. It was raining and blowing so hard the front of the shelter was wet, and it was about 40°. There was no one else around so I didn't mind. In the spring and summer I do put up my Bug Hut, but it's only slightly larger than a sleeping pad and it's never been an issue.
I have hiked into shelters before at 2AM, mostly in the winter, and most of the time found plenty of space as the winter people seem to have more etiquette. If there is no room I usually just plant myself ouside next to the shelter, making as little noise as possible. I have also stayed in them when it was overlapping pads, which isn't a problem for me. Part of sleeping in the shelter is to put up with the snorers, farters, grinders, mice, and people rolling over all night. If you don't want to put up with it, you should probably sleep somewhere else.
My brother and another friend snore, which is why I usually bring ear plugs, often quite a few pairs which I hand out. 10 packages of them, in their containers, weigh 0.3 ounces, so they don't weigh a lot.