I always wondered why Yamaha left the top edges of the disc slots so sharp instead of beveling them slightly (like your "worn" disc). It seems those sharp corners are just inviting wear into the arm ears.
You may not be able to really determine the extent of your wear issue until you fire the bike up and can check it with a timing light. The advance unit is designed to advance the timing a certain set amount, 25° when new and not worn. To do this, as the weights fling out their ears rotate the advance rod a small amount, like 1/8 to 1/4 of a turn. As the slots and/or ears wear, the amount the advance rod turns grows. This advances the timing more than the proper 25° amount. Actually, I think most of the wear occurs at the other end of the scale, at the closed or retarded position. This is when and where that sharp corner of the disc slot contacts and cuts into the weight's ear. So, the unit really isn't advancing more, it's retarding more, but the effect is the same, the amount of total advance grows. When you re-adjust the timing to correct the retarded idle setting, it pushes the full advance setting too high.
To get a general idea of how much wear may have occurred, you can look at the alignment slash marks on the little disc and the unit's backing plate. Unworn, they should pretty much point directly at one another, be lined right up. On a unit showing some wear, they will start coming out of alignment. Here's mine and as you can see, it indicates some wear has occurred. The disc slash mark is behind the backing plate one (yellow arrows). The advance rod is "closing" or retarding the timing more than when new .....
But, Yamaha took this wear factor into account and gave us about a 5° "range" in which to set the idle timing .....
So far on mine, I'm still able to set the idle timing in that range and not have it go too far advanced. It's something I routinely check from time to time and so far, it hasn't changed much, if any. Hopefully my serviced and well lubed advance unit is warding off more wear. Many condemn these mechanical advance units and tell you to shit can them and switch to an electronic ignition with a built-in electronic advance. There's nothing wrong with that I guess, besides the cost, but once I properly serviced and lubed mine up, it hasn't given me a lick of trouble in like 12 years.