My GF and I went to Cape Town for the first time last November and while we arrived at our hotel located downtown on St George mall at 10 pm one evening (and it was quite wild, with lots of streets beggars), walking in the center during the day was perfectly fine. Just apply common sense as mentioned many times before : Avoid exhibiting your expensive camera around your neck and avoid walking after dark or in our case, after the shops were closed at 6pm. There is a very good touristic bus (hop-on / hop-off) running across the region (it can go quite far and does not only stay in the city) and we used it to travel around, together with Uber. We also rented a car to go to the south cape and the country side (down to Cape Arghulas) and the drive was perfectly fine. It's a fantastic region to explore, with excellent food and great landscapes and the people we met there were very friendly. We also hiked to table mountain using the Plattekip gorge trail (if I remember correctly) and it was perfectly safe (we took the telecabin to get down though... too tired to do it on foot !). Enjoy your trip !