You will find that VB is a great place to relax. The resort has a great pool with a slide. There is a snack bar at the pool too.
The beach is beautiful too! It can get a little rough in the surf,so be careful! You can rent chairs ,umbrellas,watercraft,etc... right on the site. There are no lifeguards on Disney's beach, but at the county beach nearby there are.
There are places to see manatees, but when ewe were there, they didn't show up. We saw a lot of dolphins in the Indian River on the causeway that connects the island to the mainland, which is just north of the resort. there is also golf and fishing in the area, though I have yet to sample that.
I've seen mixed reviews on the restaurants at the resort, but I have enjoyed EVERY meal we've taken there (try the Cuban sandwich).
The area is famous for citrus too,so a visit to some of the local produce stands might be nice.
Some folks seem to like the outlets in the area for shopping. Kennedy Space Center is about 1 1/2 hours away. You can also go biking ( my wife enjoyed the guided bike trip, I slept in that day). Try to do a campfire night and have a drink on the outside patio at the lounge!
Hope you enjoy your trip. You didn't say whether or not you had kids, so I won't elabrate on the activities for them