Maybe I was misunderstood or maybe I'm misunderstanding...

vacuum boost or hydroboost it doesn't matter, they only assist you in applying braking force. Neither one has an effect with the pedal slowly leaking pressure and going to the floor. You should be able to stand on the brakes holding pressure all day long, just as if you didn't have any power assist at all. Even if your vacuum booser isn't working properly, you should still be able to apply pressure all day long. If your vacuum pump isn't working, you should still be able to apply pressure all day long.

If the pedal slowly sinks when just sitting still, you're either leaking fluid externally, or it's leaking past internally in the master cylinder.

By all means keep your power assist. I'd hate to think what a chore it'd be to stop these beasts w/o any assist at all.