Everyone has one. Batman drives a batmobile. Green Arrow has an arrow car. Blue Beetle used the bug ship.
After Night of Owls, Nightwing's stock is climbing. Higgins is proving how lucrative Dick can be on his own without needing to sport the cowl. So now he's back home in Old Gotham, funding Amusement Mile and operating from his current HQ, The Nest! How does he get around the city?
Well a bike is nice, on the flip side it doesn't offer the best security and perhaps hold as much fuel as your average sized vehicle. Practical but overused.
In Tomasi's run he flew a hang glider, a means of transportation that may have looked ideal for a hero named "Nightwing", but there was more risk than reward involved in traveling from point a to point b. He crashed it over and overrr. A simple suggestion.
Take a formula one car, customize that badboy and sneak it into his loft(should fit, F1 cars are small). If his current spot is anything like his TNBA HQ he could utilize a tunnel system that will shoot him out towards the docks or an outside sewage line, a safe distance away from home. Great way to emulate Batman but not necessarily imitate him. It's all about the car, chicks dig the car.