Just curious,

Would increasing carb size reduce vaccum for things like power brakes, vaccum advance, etc.?

Yes, but indirectly.

Too big carb might not atomize fuel properly. Engine runs crappy, and produces less vacuum. IF the larger carb still supplies a good fuel curve, there'd be no difference.

Shouldn't matter at idle, if the idle mix is correct.

The only place a larger carb will directly affect vacuum is at WFO and high RPM, and then only if the previous carb was too small.