I get a lot of my bikes from a place like that. The ratio is much better than cruising alleys but here is what I have found out of 300 bikes

20% Raleigh made
5% old chinese/finnish/greek/eastern european
20% Schwinn chicago (split evenly between ladies S7 and boom 10 speeds)
5% mixte
25% french/italian boom bikes
10% very old and either ladies/juvi or too far gone to tell
15% worth grabbing for $50-$75.00
25% too low in the food chain for right now.

all are somewhat rusty. So far from my "barn" I have grabbed '83 fuji team, '45 rudge roadster, 65 Rudge deluxe, '73 ladies sports, a pretty old Hercules with a brooks narrow professional, CLD brakes and Omelenchuk wheels. I also have from the barn a Schwinn Corvette and a ladies S7 bike with a kick-back hub. I am allowed to remove bikes and examine and shuffle parts / clean and offer for sale and/or bring them back as long as I share any rewards with the owner and be honest. (I don't "unoriginal" anything, I just take parts from "lost cause" bikes).

Once I had a good source of bikes, I quickly ran out of everything else like time and space.