For me the Cape is all about the great outdoors and its landscapes rather than the towns. There are lots of accommodation options in the National Parks and reserves (e.g. capenature.co.za) with hiking on the doorstep as well as in towns, if you are self-sufficient.
That is a lot of driving for 14 days, particularly if you spend 3-5 days around Cape Town, which I would also highly recommend with hire car to see the immediate surrounds. If you are set on getting as far as Port Elizabeth I would definitely head to Addo for at least 2 nights. The mountains and scenery are fantastic all the way along the Western Cape. I particularly enjoyed the contrast going over the Outeniqua Pass from George to Oudtshoorn. There is truly so much variety in the scenery and landscape it is hard to give recommendations! I could spend months touring the area. The beaches around Cape Town can be more sheltered and have facilities, whereas there are great swathes of coastline further east with no-one around. I think I would recommend choosing between using the highway and explore the coast between George and PE + Addo or spend 10 days touring the back routes through Bettys Bay (penguins), Gansbaai, Agulhas, Oudtshoorn (caves, ostrich farming and meerkats), R62 to Robertson / Worcester (winelands, brandy and citrus farms).
Enjoy!