this kind of sounds like what i went through about a year ago, after a lot of trial and error, my problem broke down to the seals in the master cylinder not uncovering the return ports after the brakes were released.
i know this sounds crazy, but my problem cropped up after i had driven the car at least 40 miles right after buying it. also, the prior owner didn't have this problem.
look at
http://www.tegger.com/hondafaq/mastercylinderreplace/howworks.html for a much better explaination than i am capable of regarding the return ports and pushrod length.
someone on this forum has suggested loosening the 4 nuts that hold the m/c to the booster a bit at a time and inserting a temporary spacer (i think the original post mentioned stacking quarters) until the brakes release, and then adjusting the push rod to that length.
also, there can be a lot of crud in the system, last spring i flushed and bled the system a number of times, and this winter when i drained the m/c lots of crud was in it. crud could be blocking the return ports.
good luck
nazgul