First of all, I know first hand that cars like the E46 M3 and E60 M5 can be driven in such a way that they get better fuel economy then what the EPA says they can get through a bit of experience with the car.
If a BMW M3 owner starts talking about how his car is only a 3.3l and makes more power then the V8 Mustang then he doesn't understand the arguement. HP/L is only for bragging rights and doesn't mean a whole lot in the real world. My M3 might have a better hp/L ratio then a Corvette Z06, but I wouldn't bet a dime on that race.
Supercars, and to a lesser extent sports cars shouldn't be looked at like any other car/truck/van/etc. When you buy a family sedan you consider things like price, size, fuel economy, and reliability. If these were the only things people cared about then there would be no such thing as a supercar, because the supercar is about the polar opposite of the family sedan. A Ferrari F430 costs way more then it costs to build, is small, gets terrible fuel economy, and you'll probably spend more on maintenence then gas, but to people like us none of that matters. When buying a sports car or a supercar the single most important thing should be whether or not you fall in love with the car. Richard Hammond of Top Gear described this as what makes you feel like a little kid again. I look at the sports car as the ultimate possibility for personal freedom unlike anything humanity has ever seen.
If you really want to understand the reasoning behind supercars go find the Top Gear supercar test through France. Clarkson has his GT, May has a F430, and Hammond has a Zonda. At the end of the segment they all give some great insight into the mentality behind the supercar. Clarkson is the Aristotle or Isaac Newton of cars.
Given the choice between a suped up Skyline GT-R and $80,000 cash or a Ferrari F430, I'd do the completely unsensible thing and get the Ferrari.