Upgrading fleet and staying closer to home
We've taking both tactics to heart... A couple years ago, when we were traveling from the South Shore of Boston to the Whites almost every weekend, I swapped out my commuter car (a Mini Cooper that was great fun but too small for a family of four for a weekend) for a small Volvo wagon (V50 T-5) that gets an average of about 29mpg on the highway. This was a vast improvement over our 2000 Land Rover Discovery, which was, even at the time, costing us $75/wkend in gas back and forth.
This year, when the Disco reached end-of-life (we drive cars into the ground, typically), we went nuts and replaced it with a Toyota Highlander Hybrid (getting about 25mpg highway so far). We still wanted the ability to carry 7 people, and at least modest "soft-road" capability, and we calculated the pay-back for the hybrid was well within our ownership cycle -- at $3.25/gallon. So far, it seems like a good choice for our needs.
We're also perfectly happy staying closer to home (now that home is in the mountains)... our kids love open ledges and waterfalls, but 5-mile-out-and-back is a good range for them right now, and there are no shortage of great hikes within an $8 round-trip.