I'll stay out of the futile global warming arguments, but this bit I'll respond to...
Anyway, environmental considerations aside, driving a car that gets better gas mileage has two concrete benefits:
1: your nation has to buy less oil from OPEC, which means a better trade balance for your nation and less money for the OPEC nations (many of whom are accused of sponsoring terrorism or oppressing their populations--I leave you to judge for yourself the truth of those claims).
A "better trade balance"? Trade today is a zero-sum game. If your country spends $5 billion on oil, it gets $5 billion worth of oil in return. The only way for a country to have a negative trade balance is to subsidise trade, in which case it either sends its goods abroad for less than they're worth, or imports goods for more than they're worth. But then, of course, if you buy stuff from another country which subsidises exports, you end up getting more goods than your money's worth, so everything evens out in the long run.
Trade balance used to be very, very important - back when money was more than mere paper, and when it wasn't possible to make large transactions electronically. In the 19th century, money was more valuable than any other commodity, so having a negative trade balance was not only possible, but also a huge problem. A negative trade balance meant that physical money (gold and silver coins - which obviously cost more than paper money to produce) left the country, and if this carried on long enough, the local economy was affected simply because people had no actual money to buy things. This caused deflation, which in turn meant that when you exported goods, you got less money for them than they were actually worth. Today, however, all this is virtually irrelevant - most transactions require no cash at all, so it would be next to impossible to deplete your country's cash supply to the point where the economy might notice it. The only reason people still keep on talking about trade balance today is because of how dominant socialism has become - and of course, a socialist will always tell you that it's better for you to buy locally-made products than imported products, even if the latter are cheaper and better.
2: You have to buy less gas. Let's do a back-of-the-envelope estimate here. Let's say that you drive a standard sedan that gets 28 miles per gallon in real-life driving (as opposed to the idealized sticker mileage). Now let's compare that to a hybrid getting a modest 25% more miles per gallon (35 in this example). Let's also say that gas averages three dollars per gallon over a 100,000 mile lifespan of the car. The standard sedan will consume approximately 3,571 gallons over this lifespan, while the hybrid will consume approximately 2,857 gallons--you save 20%. At three dollars per gallon, you save about $2,150 in gas, as well as being able to drive 25% farther between fill-ups. If and when hybrids can sell for only a couple grand more than full-combustion vehicles, it will be to the customer's economic advantage to use one.
A hybrid car may indeed be more fuel-efficient, but I'm not convinced it's actually cheaper. The US government is pumping money into hybrid technology like there's no [oil] tomorrow - and the government has only one source of money, which happens to be
you. Of course, they offer you tax deductions and other incentives for buying a hybrid car - but such subsidies are generally just tricks, with the government taking $500 from you with one hand, and giving you back $400 with the other (and in any case, such benefits are purely temporary - you might get free parking in LA now for having a hybrid... but if another 100,000 people in LA buy hybrids, the free parking will have to go away). There's no such thing as free money - any government intervention in the economy is harmful and ultimately costs you more money than it's worth.
Don't get me wrong, though. Hybrid cars seem like good technology, and in all likelihood, they'll be the way to go in the future, even if governments decide to stop spending my money on promoting them - but you should always be aware of the hidden costs.