The Plus package functions as a prepaid bar tab plus access to a private bar — meaning shorter lines, which matters because the main bars downstairs get backed up. Past Plus packages have included a buffet station (charcuterie one time, loaded tots another), and a behind-the-scenes tour of the facility. The drinks are described consistently as small but strong. The rainforest dome closes around 8pm, so if that's on your list, get there when doors open, not after your second drink.
The base Nightlife ticket gives you the aquarium, planetarium shows, and the main floor — the bars near the aquarium level tend to run shorter queues than the central ones upstairs. The Plus bar is the practical fix if you hate waiting in a line holding an empty glass.
If you have two hours: arrive at 6pm, go straight to the rainforest, then head to the aquarium level bar before the crowd migrates down. You'll cover the best of both without fighting for a drink.