In Costa Maya I would advise you to get away from the port. It is basically one big shopping mall. If you like that then that is the way to go.
Last year we went to Chaccoben Ruins and the Seven Colors Lagoon. It was a fun day and the ruins are very interesting. More interesting than Tulum, IMO and I recommend it.
We have also went into Mahjual (sp) and just walked down the street and bought a few things from the street vendors and stopped and had a drinks in one of the bars. You can do that in the Costa Maya Mall, actually they have Senior Frog's there but I just liked the atmosphere in the Mahjual bar. Plus the drinks are half the price or even more than that lower than you will get at port.
I really don't have any information on the zip line.
Take care and have a great cruise.