Chris,
They did that to me too. I called them up and said "No Thanks" and they gave me my money back, and I switched to TACA, who has a virtually identical redeye to SJO. They ought to do the same for you, if you're willing to fly TACA/Lacsa. I'd rather put up with the baggage nazis than extend my flight time that much.
As far as land tours, I did two: Did the "all day" Rainforest Canopy Tour offered through the hotel (Grano de Oro - nice, worth the $, make sure your room has A/C if you run hot. Most dont', but it's not THAT humid there, or atleast it wasn't in April.)
The canopy tour was pretty fun, but not like super amazing. You tended to get herded around a bit (there were like 10 of us), so I didn't have much time for photography. It was also raining, and I didn't think to take my housing along on the land tour . . .
I also took the "4 in1" tour (after we got back the last day). It was more interesting, but still pretty "not in depth". That one is written up in guidebooks. The hotel/boat can arrange them for you.
The best thing to do would be to rent a car and drive yourself around - costa rica is easy (well, it looked easy to me, but I wasn't driving). Then you can stay at the Butterfly Farm (great!) as long as you want, instead of "hurry hurry, it's time to go to the volcano". And the active volcano is pretty interesting too, but not so interesting that I still remember its name. The little jungle river boat ride was . . uh . . . pretty quick. We did see a real live Crocadile in the wild though, that was cool.
I would say, rent a car and drive to the big rainforest canopy national park. Take the zip line, take the canopy tour in the little tram (with a guide), go on a hike there. If you have more time, hit some other stuff near there.
Oh, you said Cocos Island land tour. oops. Well, I'll leave that other stuff up anyway. I wouldn't do it if you have to skip diving. Maybe if they offer it on a beautiful sunny day, dunno. The park rangers don't let you hike to the waterfall with the diving pool anymore, so the trip to the beach was kinda soso. They did it on one of our surface intervals though, so it was good. Tevas are probably fine if you're comfortable walking up to maybe half mile in them. I just hung around the "beach" (it's rocky and dirty). I think most people wore their dive booties.
The SH boats have kayaks, one guy made alot of use of those during the (long) SIs. The rest of us just fiddled with our cameras.
I didn't take one nap, and I did three dives a day deeper than 90 feet, pretty much every day. I love nitrox!
So what else?