I would definately replace the sticks. I used my X-Arcade for about 6 months with no complaints. Then I traded some old WICO joys I had for some Happ Comps. Big difference! The diags are much easier to hit with the Happ. I have also used the Happ Super and feel it too is superior to the original X-Arcades.
Comps have a very light spring and require some getting used to. Supers have a heavy spring.
Also want to mention, I don't think the Happ's provide an authentic "Arcade feel" either. They do come much closer than the X's though. To get the original feel, you would probably need to go with some Wico leaf's.
As far as the buttons go, I don't think you would notice much difference there, although the Happ's do feel like a higher quality...may have to do with the spring used.
Xam