Me and my fiancee talked about it one point, she collects stuff also (mostly dolls of course but has a good collection of Who Figures). It's no different than buying say paintings, or ornamental decorations for the house. It's often an easy way to kind of show interest in shows or things you like. For some reason many have gotten the idea that toy collectors buy stuff to play or it's some how they are stunted in growth, oddly enough it's OK to buy things that are somehow deemed adult but are often really no different than the way we use the toys we buy.
My fiance doesn't see either of us kids per se, it's more decoration for us. She has done some photography with hers here and there, but it's not like she pulls them down and has tea parties with them. It's the aesthetic we are drawn to, and sometimes the ability to kind of tell a story through that aesthetic that can be changed to what we would like. I was better at I would have mine posed more, battle scenes etc, but the way I have them displayed etc doesn't really allow for that. Fiance has said she would like to have some of the playsets etc for similar reasons (playsets often being over priced for what little you get with dolls).
I have had many male and female adults say it's no different than their spoon, stamp, shot glass, dish, statue, carving, movie, shoe, postcard, etc collection.