Frankly, as a Park Slope resident, I don't think there is a down side to this development when it comes to the leafy side streets of brownstones. Fifth Avenue and Seventh Avenue are already packed to the gills with late night restaurants and bars, weekends rollick all the way down to the Prospect Expwy so there should be little change in those directions. If anything, some of the recently shuttered businesses (a few old school jewelry and appliance stores) will probably reopen in the same upscale vein as has occurred over the past decade, gastro pub style.
Fourth Avenue will probably be changed the most down towards Union, a divided four lane "boulevard" with plenty of parking and the potential to transform gas stations and vacant lots into housing with retail bases, exactly what it needs and was re-zoned for. Only a few of these bases are needed to create a sports bar/ post game club row to handle those wanting to revel in the wins and defeats. Plus that divided part of the avenue hosts a subway, win, win.
Flatbush NW from the arena has plenty of room, too, for bars and clubs bleeding into Fulton Mall and of course, Juniors. Juniors is already a late-night after club bastion so they must be thinking about expansion.
So I really don't think the Park Slope of quiet, brownstone literary couples has anything to fear. Sports fans will go where the nightlife is, most of them will be using the subway and nobody is proposing (nor would it be legal) opening bars and clubs in the basements of brownstones. The worst that might happen is a few weeks around the Nets making the playoffs and playing in the championship (lol). By the time that happens I'll bet most Slopers will be proud fans of the home team! Park Slope is becoming more diverse every day.
I know a slew of these Park Slope "literary" couples who are already anxious to get their hands on tiny "Brooklyn Nets" jerseys for their toddlers. Little, mixed race, first gen American fans of the Nets- who would have thunk?