well firstly bleed the system and see if you can get a good feel out of it BEFORE you decide to start spending money here and there. there have been many cars come into my work with sticky or rough feeling clutches, and the answer was simply some fresh fluid. as you will know, the brake fluid used for the clutch seems to become dirty a lot quicker than what is used in your brake reseviour, simply due to the amount of useage. you say that it only started getting sticky not long ago... then personally i would be bleeding and checking the system for loose lines (air leaks etc) before i go spending money.
if that doesnt work watsoever, then the guys above have given you the straight answers.
good luck!
