When it comes to sleeping in armor, there are those who want to emulate read-only fiction:
"He stood up and cast open his long black cloak, and behold! he was clad in mail beneath, and girt with a long sword, great-hilted in a sheath of black and silver. ‘Thus have I walked, and thus now for many years have I slept,’ he said, ‘lest with age the body should grow soft and timid.’"
- Lord of the Rings, with 'he' being Denethor.
But armor is just an instance of a more general problem: Balancing options between "good enough that everyone takes it" and "bad enough that no one bothers with it." In the case of armor, this becomes "loads up on as much armor as the PC can afford and their class allows," and "avoids all but the lightest armor - and maybe even that." Not to mention "everyone lusts for the 'special' armor that has reduced penalties for its level of protection (cough mithral shirt cough)"
One possible solution (in the case of armor, at least) is an improved armor proficiency system of some sort.