I can't tell you about the experience you might need, but as a geography major applying to MA and PhD geography programs, as I've been looking at the CVs of the faculty members at schools I'm interested in (and the profiles of their current PhD students), I've found a surprising number who didn't study geography for undergrad. For example, look at the current geography PhD students at Clark: http://www2.clarku.edu/departments/geography/graduate/current-students/. Plus, considering how closely related urban studies is to some disciplines of geography, I don't think you should be too worried about that part of your background (at least from what I've learned so far in this process).