There are several tour companies that offer day trips to Valpo/Viña. And, there are some terrific wineries on the way that are worth visiting.

Another option worth considering is Pucón. To get there, fly from Santiago to Temuco and then either take a bus or rent a car. Pucón is one of my favorite cities in the world, offering beautiful Lake Villarica, fishing, hiking, white-water rafting, horseback riding, volcano climbing (!), a casino, and more. I take a group there every year and it's always the highlight of our time in Chile.