I have very often opened my eyes at the end of a song to find a full room.

I think this is a personal preference, like boxers or briefs. Some people are going to like it, some people aren't, others won't care one way or the other.

My personal opinion, is that a performer should be him/herself. If that involves closing your eyes, fine. The audience can tell when you're sincere and when you're not. When you're sincere, they appreciate it, eyes open or shut. So there.