It is a win-win situation so just do it. It really is an insurance against future gas price, $5 and beyond. Plus, you'll feel less stress on your commute. Trust us on that one.
Is your 35 mile commute mostly highway? If so, you'll likely find that you can get even better mileage with a Prius Hatchback (not the Prius C) because the 1.8L engine and the aerodynamics are more condusive towards attaining higher highway mileage. Yes, the price will be more expensive, but I suspect that there won't be many price breaks on the C when it comes out (due to popularity AND that gas prices are predicted to peak around Memorial day near the $4.50/gallon mark) and you can get a Prius hatchback now. Just a thought.
unless you drive alot numbers never work out in favor of having 2 cars instead one. As 2nd car in 2 car family? yes! As replacement car? hell yes!