I see this a little differently. To me, vacuum advance is not just an economy measure it's an efficiency measure. Two byproducts of more efficiency are better economy and more power. If a motor wants 30 degrees of timing at 3000 rpm under full load wide open throttle and you only give it 26 degrees it will be less efficient and make less power. Same is true for part throttle at 3000 rpm under cruising load if the motor wants 40 degrees and it only gets 30 degrees it won't be as efficient.
