We've done the THV both with and without a car. It was certainly easier with the car, but not inconvenient without.
In general, I find the buses at SSR to be the most consistent transportation of any
DVC resort. (At other locations, there's great transportation to a few parks and terrible service to others. A shiver just came over me thinking about the buses to MK/AK at BWV and BCV.) There's good service to all locations from SSR.
That said, when we have a car, we will drive to every park except MK. I really hate dealing with the T&T Center, so we almost always use Disney transportation for the MK. We'll drive to all the other destinations. (Sometimes we'll do the boat to DTD.)
Now, to the specifics of the THV. Drive when you can. If you do take the bus, consider walking to the Grandstand. It isn't extremely inconvenient to use the THV buses, but you can probably walk to Grandstand quicker than waiting for the bus. It's not far at all. This also puts you at the first bus stop on the theme park route instead of the last.
Others have recommended driving to Grandstand to catch the theme park buses. That works, too. There's plenty of parking near the Grandstand bus stop, and it is the parking lot Disney designates for THV guests with more than one vehicle. For me personally, though,
I'd rather keep my parking spot at the THV and take the quick walk.