My buddies and I created dummy accounts to spoof just to see what the situation was like in really high populated areas like central park. More of a testing ground than anything else to try and confirm some suspicions about rarity vs user density. Our findings definitely showed a direct correlation between the two. Managed to hit level 10 and get nearly 50 unique in about an hour. The variation is what blew my mind. You see every type regardless of the location. It definitely led some credence to the theory that the more people you have in the area, the more varied and rare the types of pokemon you see.
Honestly, I can't see the fun in playing like that. It gets so boring. It also just made me irritated that I was getting things at such a low level that I'd never even see in my current area.
It's mostly how I play during the week since there's barely any stops around here and the same 5 pokemon constantly. Can't justify driving 30-40 minutes to lured pokestops every day. Had they designed the game with players in low population areas in mind then I would gladly go for random 15-20 minute walks around my neighborhood playing. I'm more into the collecting aspect than the gym battles anyways.