I recall reading about wheel caused vibration issues a while back on Camaros.net. The problem was with wheels that are located on center by the studs instead of by the center hub. Granted these were used wheels, probably with worn mounting holes. Just for grins, jack up each wheel and spin it by hand and watch. Who says a brand new wheel has to be concentric?

The reason a master can cause this issue is there is always a small amount of rotor run out and this run out will normally kick the pads back into the caliper. If the master cylinder holds pressure against the shoes (say it was a drum master) , the rotor can't kick the shoes back so they will drag each time the rotor high spot passes. The high spot won't be high enough to cause brake pedal surge but it is enough to cause vibration if the pads can't retract. It would be typical for this vibration to be worse as the brakes heat up. It's a long shot. I would look at the rotating assembly again first.

It probably won't help, but you could try torquing the wheels like you would a cylinder head. With my Fords, I'm used to that procedure because the tire shop impact wrench method warps the junk Ford rotors right away.

Front end vibration shouldn't be ignored. It puts the front end parts under increased stress so parts will wear out quickly. Maybe you can find a specialty shop that will look at balance and runout issues while on the mounted hub. Before computers told monkeys where to add weights, they would spin problem wheels mounted on the axle at speed. There are transducers that can be mounted at each axle to isolate which one is the cause.

Check the wheel bearing torque too. Loose bearings will make the car ride like a worn shopping cart. If they were overtorqued, they may be damaged now. There is a sweet spot for these bearings which Amervo described in great detail a while back.