Rear Disk or Drums

I have 10x2 oem rear drum brakes(with the KH discs up front). In 15 years of street driving, and 125000 miles Ive never needed more.IMO, for a street A,drums are more than adequate. Why do you imagine theres a proportioning valve in that rear line?If youre installing much bigger tires in the rear, then you might be able to take advantage of more braking power back there.If not, then not. Too much in the back, tends to put the back in the front, at the worst possible time.
And I agree on the pricing. $350 sounds awful pricey.