We just returned TODAY from the same cruise - 5 nights on Grandeur. At Costa Maya we had reserved a catamaran/snorkeling excursion thru the ship (didn't book it until we were on board, I think it's something new they added). We got off the ship & hung around the port until time to meet (2:30) and found out that it was cancelled due to choppy waters/undertow. Our Plan B was renting a golf cart ($30 for 2 hours). We actually enjoyed that alot because it took us away from the cruise-line manufactured port and into the REAL town. Once there, you can rent snorkel equip., get a massage by the water, and just drive around & see how the real people live. Our table mates did the jungle tour & they weren't real thrilled with it.
On Cozumel we had arranged for a tour on our own through cozumeltours.com We were with Nelda for almost 6 hours ($60 a piece for the 2 of us) & we thoroughly enjoyed it. We saw the whole island & had lunch at Coconuts. Also went to the ruins at San Gervasio.
We tend to avoid the cruise line tours if possible and this trip that worked out well for us.
Let me know if you have any questions about the cruise - it was our 6th but first on Grandeur & 1st to Costa Maya & Cozumel. The ship has seen better days but was okay all-in-all.