Hi. To reply to your posted questions--yes--it was splash dive ops. It wasn't the most amazing of dive ops, but the diving was good--we were out at laughing bird caye. The boat is small and if it's rough, your back will hurt. We did do a monkey and manatees tour--also through splash. Our local guide was awful (didn't speak english or spanish and he got us lost--kind of part of the adventure), but inspite of him, we saw monkeys. Our boat guide had amazing eyes and spotted so many critters for us! We saw a lot of manatees, but didn't snorkel or dive with them. Was cool to see them though.
As for the cave tubing--I have done it through Ian Anderson's and it was fun, but like i said, we were there in 2000, so don't know how much it has changed. We went to the Crystal Maiden Cave in 2004. That was not cave tubing--it's wading and swimming though this cave after a walk through the jungle (not too far 1/2 mi. or so) and prior to that, an interesting trip to the jungle. The formations in the cave, the pottery and the mayan ceremonial sites make this trip worth it (IMO). We scheduled our tour through the cafe in San Ignacio where all the expats hang out--they are famous for organizing tours in the western part of the county. Rosies? If you look on the main belize websites you will find info on it. Tikal was pretty amazing too--we did that as an overnight trip. Xunantunich (in western belize near san ignacio) is neat if you aren't too familiar with mayan ruins (after you see some of the other bigger sites, it's not quite as amazing--but that was the first one we saw, so we were pretty wowed). I really like the western part of belize, but you have to go with the group preferences. We always do a dive trip and add inland stuff to it, but that's just how we like to travel.
It's a fun place. Placencia is a fun town, laid back, not completely touristy. We went to the most insane halloween party when we were there. Very jealous you are going so soon!