Leaving off the spare wheel, and bracket, wouldn't even give you a 5% improvement. (Come on, some one prove me wrong.) So would that be worth it?
One method for getting better economy I heard of was fitting a much stronger throttle return spring. With drive by wire throttles you'd need to fit that to the pedal and not the butterfly.
Take those tyre pressures up to the mid to high 30's (psi) (check tyre wear to find optimum pressure though) And get that wheel alignment checked and spot on.
It varies from state to state on the legality of driving without a spare. But if you upset Mr Plod on a bad day he may issue a vehicle defect notice for it (original equipment for roadworthy must always be present and servicable. (But who checks?))
