They round up people from the resort around 10pm. The vans pick you up at 11. They take groups to the clubs. You are responsible for your own ride back. Its like 60/pp and its all you can drink bottle service and VIP type seating. No waiting in lines outside. You get a table too. Its different clubs different nights.
We've never done the clubs. We always find it hard to leave the party at patio. We would like to check out coco bongo the next time we are there, we heard it is quite a show to see.
The OP specifies downtown Cancun. Let's be clear....the clubs in HZ are not in downtown Cancun. Complete Opposite direction to downtown. The HZ is safe unless you run into some tanked tourist looking to cause trouble Downtown on the other hand has alot fewer gringos and some areas are sketchy. In fact some locals don't like to see tourists downtown at night.