Also consider day trips to the Maipo Valley. Your hotel should be able to arrange this. It will probably be in a small van and won't cost an arm and a leg. Probably one winery in the morning, one in the afternoon, lunch in between. Guide should know enough to add value. (Each winery will have its own guide in any case). No designated driver issues, no worries about showing up at a bad time for a public tour, and you save a day's car rental/fuel. Then, pick up your rental car and head for Viņa.

(The wineries give you your tasting glasses, etched with their names, as souvenirs. Pack them carefully.)