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Aside from safety regulations, there's nothing really stopping cars from having good performance. A large engine needs not be significantly thirstier. Good example would be the BMW 328 (with N52, Valvematic and double VANOS), which gets great fuel economy for a car that's not exactly lightweight. Throttling loss is the biggest reason why bigger engines are bad fuel economy wise. Now if the displacement is too high like the Nissan VQ37VHR then it'll have a bit of trouble naturally, but extremely tall gearing can almost fix that, as the Mclaren MP4-12C proves.
The benefit that increased efficiency provides is that manufacturers can afford to tune the engine more aggressively at max power since the better fuel economy/emissions at lower loads will offset the less efficient operation at high power. Lighter cars are no doubt better for performance, and better aerodynamics help as well.
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