Many families manage very well with a hybrid compact sedan (Prius, Civic, etc). A PHEV sedan could be close to perfect.
The more important point to consider (IMO) is the economic tipping point for widespread adoption:
If the Volt *saves* the guy in LA $160/month, that's ~$2000/yr. If he keeps the car 10yrs, he effectively paid $10K (30K(-20K)) for a car that uses little fossil fuel.
- People are not going to drive less.
The cost of the cars will drop as the volume increases and the price of gas will rise with global demand and the cost of crude.
The company that has the most cars available to the growing market wins.
The country that spends less on fuel has more capital to buy goods and services.