Donna,
While Alan may prefer to spend those 4 days in the Winelands which are magnificient, Cape Town has much to recommend as well. For nature, there are the Company Gardens and (sp.?) Kirshenboch Gardens, Table Mountain and the Cape Peninsula with the park and Simonstown/Boulders Beach with its penguins and Robben Island. Remember that with jet lag the first day may seem a loss anyway and the 4 days will not be too much in Cape Town. Or maybe split your 4 days? An overnight in the Winelands would be great too. Such tough choices! I don't think you will find that 4 days is too much time to spend in Cape Town or in the vicinity.
Good luck, Debbie