[Vicegrip]

Originally Posted by Roo

Hmmmm....sure sounds like a master cylinder spool seal failure. With a well operating brake system, pushing the brake pedal pushes a spool inside the master cylinder bore which forces fluid from the reservoir through the lines into the brake calipers moving the pistons againt the brake pad backing plate.
The spool has several seals which separate the two halves of the brake system and force fluid into the lines. When the seals fail, pushing the pedal doesn't transfer as much fluid (or pressure) through the lines to the calipers resulting in reduced braking. Pumping the pedal may help as you're resetting the spool with fluid from the reservoir.
If you lost the vacuum boost on an otherwise good brake system, you would still have a functioning brake system. However, the pedal effort would be much higher (and the pedal wouldn't go to the floor).

This would be my first stop given the list of issues. Let us know what you find.