New top mounts make a whole universe of difference!
I'm constantly having to have my tracking done, it goes out at the drop of a hat 
I paid a lot to have mine done at a vw dealership in sheff once, and it went out after 5 min and they didn't leave the steering wheel straight 
Kittie, once your tracking has been set, it shouldnt go out of adjustment, unless you hit a kerb or a deep pothole! I would say that you may have other suspension problems, if your getting uneven tyre wear, or short tyre life, you may need new shock absorbers, bushes, or ball joints, not necessarily all 3 at once though! another possibility is that the person doing the tracking doesn't actually know what there doing! thats more common than most people realise!
Tom