But the "monsters" and locations would be different based upon your demographic/interests. And people could incentivize a certain type of person to go to certain locations.
The app could also access your personal information such as age, gender, hobbies, finances, etc.
Imagine you're a Jeep dealership and you're having a huge Jeep sale. You drop some bitcoins right smack dab in middle of your dealership and let the app summon 20-40 year olds that are into outdoors/Jeeps.
Or a nightclub instead of ladies night putting some bitcoins inside the club to attract 21-25 y/o females. Even some rich guy could drop some near him to get the ladies to come over.
A strip club that puts some bitcoins attracting males with good finances to come in.
There could be some sort of beacon that draws people toward the place which might be brighter for more bitcoins, beep faster as you get closer. Maybe have it take a little while to "mine" the bitcoins in the location so you're apt to stick around a bit (and do some shopping/browsing).
I think this isn't a bad idea. People love free money. In order for it to become actually viable with the types of people you're talking about (clubs, dealerships, people selling things) then bitcoin would have to become a large bit more popular and accessible. As easy and fun as bitcoin actually is, a lot of people still just consider it "for hackers". Nevertheless, I think your idea isn't too bad.