Just got back from Cape Town (five days) on Thursday. I seriously don't recommend the rental car unless you're dying to do it. Ubers were very quick and cheap as well (unless I guess your group is too big for one vehicle). To give an idea, we took an uber from Table Mountain's cable car point down to the V&A to go shopping after hiking the mountain for a couple hours. It was a less than $7US for the ride back down.

Even our Uber Black trip from our AirBnB to Constantia for dinner (30 minute drive) was $21 one way. The return trip in an Uber X was $12.

We just hired someone to drive us to the wine region and Point of Good Hope, which was so much better because she was able to tell histories and all on the drive (and after wine tastings in two wineries, we shouldn't be driving anyhow).

For the price I'd say, skip the car, hire a driver just for the day while you're going to wine country. We used Luhambo Tours and can't recommend Marlene enough.