Downtown Greenville is nice for a walk. There is a pretty park along the rivere with waterfalls. We didn't do much else in that area, but the concierge (several of them) are extremely helpful. They know all about PCD and go out of their way to take care of BMW people. They pick you up at the airport in a BMW, they will give you a ride downtown and pick you up (all in one of several BMW they have). The food at the hotel was actually very good so don't eat out to avoid "hotel food". We were impressed with dinner there even off the BMW selected menu.
For PCD be sure you take a camera, but I was too busy to remember to take photos. Wear comfortable shoes - the factory tour was great but a pretty good walk. If you get motion sickness, take something for it. The track experience gave me some discomfort. The hot lap with one of their race car drivers in an M3 is totally wild. Be sure to be ready on time. They have a busy schedule and they work to stay on time. You should be done by about 3pm. The whole day is amazing. They take great care of you and everyone is SO nice.