Pat is correct...if you are a renter, you get the shuttle for free.
Vistana shuttles (time and destinations) are limited. They do not go to Universal or Sea World---only disney parks on a rotating basis. This was the shuttle schedule the last I checked :
The shuttle service is as follows :
7:55 am
9 am
11 am
12 noon
then pick up later in day :
4:30 pm
6 pm
8 pm
9 pm
and at park closing
For the morning rotation (I didn't get the evening rotation):
7:55 am MK and AK
9:00 am MK and MGM
11;00 am MK and EPCOT
12:00 pm ALL parks
So you can't pick and choose which parks you want to go to on whatever days you choose. They don't go to the disney water parks. You'd have to get there via a cab or catch a bus from a park or resort. I would NEVER rely on the shuttles at Vistana. If I didn't have a rental car, I simply wouldn't stay there. Now on disney property, I'm fine without having a rental car. According to Vistana, the earliest you could ever get to Epcot would be noon.
Hope this helps.