there's not a whole lot involved in the clutch system. you have the clutch master cylinder, then a rubber flex line to your slave cylinder. which pushes on your throw out bearing which presses in the pressure plate.
the pressure plate itself shouldnt cause this, and if anything over time would get softer.
im thinking it could be the rubber line itself between the master and slave cylinder. they can expand over time, and actually almost block all fluid from transferring. that could cause this sort of issue. if thats not it, the next thing id be thinking is possibly a throw out bearing getting hung up.