Bigger exhaust will actually increase your fuel average; coz other road users would clearly hear you coming from distance, you'd earn their respect with your loud screaming petrol headedness, and they'd happily clear way for you.
Lesser brakes = more fuel economy.
This works just as well for awesome dazzling HIDs- after all, some one spending whole 5k on lights alone definitely deserves to be taken seriously. It's a humble way to say: 'Clear the way losers! I've got HIDs I rule the road, fags' - much humble though. Respect!