Well, in my case (EQ6 classic) I had (and still have) a problem with transfer gears (47-teeth each..
http://www.iceinspace.com.au/forum/showthread.php?t=43823&highlight=Eq 6+belt+modification), which are causing 3-5 arcsec "noise" superimposed on the general PE curve (caused by worm gear and meshing). This is going to be reduced by timing belt & pulleys (already in the queue, just need some spare time for this)
I don't think my mount has any other issues that can't be sorted out by autoguider.
So, before you start, you have to know exactly where your eventual problems are (if there are any). Otherwise, the whole exercise could turn into expensive affair, with a lots of hopes and not much gain...
Try to use k3ccdtools, it will produce a plot of your mount PE, from where you will see what is going on and how bad it is (
http://www.pk3.org/Astro/index.htm).
And, yes, only tapered bearings (and those 2 on RA worm) are important.. the others do not turn at all during tracking, so I would not consider them for replacement at all.