Yes, servicing the advance unit, advance rod, and most importantly, the bushings in the cam that the rod turns in should be considered routine maintenance, although I've never seen it mentioned as such in any of the manuals. Many of these, if not most, haven't had this done since they left the factory, lol. It doesn't need doing often, like maybe every 5 to 6 years, but it does need to be done periodically. The factory shop manual recommends a grease with moly in it. I use VW CV joint grease because it has a very high moly content. The bushings in my '78 were pretty much dry when I got it, probably never serviced since it left the factory. Here's some pics of when I re-serviced them 5 or 6 years later. There was still a bit of grease left in the grooves but I repacked them anyway ......
The grooves in the I.D. of the outer bushing are there to provide a reservoir of grease for the advance rod, so pack them full.
Now let's talk about advance unit wear a little bit. When these are new, they're made to advance a set amount, 25° I believe. As they loosen up and wear, this amount starts to grow. Now, I've never encountered wear to the center disc slots like you and DogBunny have, mine is the more normal kind I think, to the little tabs on the arms. There are alignment slash marks on the little center disc and the advance unit backing plate, and on an unworn unit, they should point to one another .......
On mine, as you can see, they don't (yellow arrows) ......
I think what has happened on mine is that the sharp corners on the little disc's slots have cut into the side of the little tabs on the advance arms (top arrow) ......
This allows the little disc to "retard" more, throwing off the alignment slash marks. So, while my unit may not be advancing more, it's retarding more and that has the same effect - the total amount of advance grows. I think Yamaha took this gradual advance unit wear into account and that's why they speced the idle timing as a "range" instead of one set number. Even though my unit is worn, I'm still able to set my timing correctly, at the right side of the "range" at idle but have it not over-advance at full advance. The wear hasn't increased at all since I've had the bike, probably because I routinely service the advance unit and keep the advance rod lubed.