Good point, but it seems they've been in place for decades and have had heavy mirrors hung off them. They were probably fitted by someone who knows what they were doing.
The walls probably aren't as bad as I make out - I'm also rubbish with a drill and end up messing up things like this...
Wouldn't the picture rails be attached to same said cheese? I would be worried about them coming off and the guitar(s) coming down too.