I went to Cabo for 5 days in July and going back for 4 more in November. We LOVE it there. Partly because it's a quick 2 hour flight for us here in DFW
Yes, go down to the marina area nightly. That's where many of the restaurants and bars are. Like you mentioned, Cabo Wabo, Senor Frogs, Happy Endings
Cabo is great because it is a place where you can just relax. We stayed at the Fiesta American about 7 miles from town and it was amazing. I'm a golfer, so I play golf while I'm there as well.
Snorkeling..ehhh.. I guess depends where you go. We went to one spot and it wasn't very great, but still had a fun time.
I would recommend eating dinner at The Office down a couple blocks from the marina.
Cabo is a great place to relax at the pool and beach during the day (maybe a round of golf) and then go out to dinner and for some drinks in the evening. There is also the dune buggies you mentioned. I'd like to try that myself.
Also, consider renting a car and driving around. There are a couple towns within an hour or so that may be neat to go to and have been recommended to us. We are going to do that next time we go.
if you have anymore questions, let me know!