I hang my guitars for the same reasons, and I have for years. I cannot attibute any playability concerns to the fact they were stored hanging. And in the case of my acoustics, it may actually have served to hasten the "warming" process.

Hanging in the open does expose your guitar to more environmental change than being "buffered" in a case. This would have some impact including quicker deterioration fo your strings, finish, movement of parts due to temperature & humidity change etc.

Ideally they should be stored in a case, but to me, if it makes me less inclined to play then it is not worth it. I bought them to play not to store. :)

Definitely keep them out of direct sunlight, drafts, try to use interior walls, etc.