My dd studied ancient mayan civilizations in 3rd grade, so we planned a western cruise so she could go to the ruins (like we needed that excuse!) Since ds had NOT studied the ruins (he's only 7) my dh took dd to the ruins alone.
They enjoyed it a lot. I'll recap the pros and cons from their POV. cons: the trip from the ship to the mainland was about 35 minutes in a ferry boat with very high waves. Then the 1/2 mile walk and the hour bus ride, then some sort of tram ride to the ruins. There was the cheezy gift shop stop, although my dd did buy something for my ds there and was excited she found him something. They serve lunch on the way back....subway sandwiches, chips and either pop or beer. They give it all to you and expect you to manage that on your lap (with a very full glass of liquid) on a bumpy trip.

The beach you get to stay at had no chairs, no umbrellas, and no where to set your stuff. Dh ended up holding everything while dd played at the very edge of the water--couldn't go any farther b/c of very high waves. The beach had lots of Mexican kids swimming in their underwear. The tour guide they had droned on and on and on. dh and dd occasionally walked away, sat in the shade of a tree, then came back feeling like they hadn't really missed anything.

pros: they were able to see the magnificent mayan ruins!! they were able to tie in everything dd had learned and i'm sure the experience at the ruins will help solidify that in her mind. they had fun being together --just dd and dh-- for some quality time. they'd got an awesome picture of the two of them at the ruins.
all in all, even though the list of cons outweighs the pros, they were both VERY happy they took the excursion. in the meantime ds and i did a dolphin encounter in cozumel and although our list of cons outweights the pros, we too ended up VERY happy we took that excursion. once getting in the water with the dolphin, all the headaches of excursion logistics seemed to float away!
to note....my dh and dd made it back JUST in time for early dinner. they had to wait in a long line to get back onto the ship (the ferry disembarked and most of the ppl were heading to the Magic) they literally got to the room, threw on dinner clothes and went to dinner.
HTH