We've had good BWV bus karma, but it seems we are rare.
A rental car is quicker.
Another plan is to take a cab in the mornings - take it to the Poly and grab the monorail. Saves on car rental if you aren't going to the MK often. We then take the monorail back through Epcot (need hoppers), make a swing through Future World, and walk back to Boardwalk.