I definitely agree with this. I didn't have a minor in undergrad but I did have a second major which was theater. While it may not be as related to psych as some of the sciences, a few of my interviewers actually brought it up. Some brought it up mainly as curiosity (ie: that's an unusual combination, why theater?) Others brought it up and commented on it in a positive way. I want to work with children (which was indicated in my SOP) and the people that commented on it in a positive way generally said that they think having a theater background would be very useful in connecting with little kids (and I have a hell of a lot of fun role playing clients with classmates
).
I do not think that a lack of a minor/2nd major will hurt, but having one may help a little bit, perhaps moreso if you can tie it in with psych. Even if it's kind of an unusual combination like mine sort of was, interviewers remembered it and if it's a positive thing that makes me stand out a little more, I'm all for it