I've been hesitant on monetizing because of that very same growth I'm seeing. In about 6 weeks I expect to peak in the top 10 US Navigation app for about 3 days (new school year).
I've been debating ads + freemium "ads free mode", but I feel that at this point I'm getting more value out of establishing a user base. My real issue is that I don't have a GOOD scalable monetization option in mind.
Negotiating local deals takes way too long with too much turnover. I'd be interested in offering school apparel deals though. That seems scalable with the right vendor.
e: I am currently split testing one campus @ 99 cents in a separate app to test how that's received.