You can repair the holes by oversizing the holes and fitting bronze bushes. To do this the hole must be machined in line with the cam, attempts to drill the hole out will usually result in the hole running off. The job is best done on a mill with the head set up true to the cam, using a small solid carbide boring tool (reaming to size if required)
If the wear is not too excessive alternatively another fix is to just oversize the holes and bushes to say 8.3mm (or whatever) and make some oversize spindles. Small oversizes can be achieved with hard chroming the original spindles.
I have used both the above methods to perfect effect. It is essential if you are oversizing the holes to any extent the alignment should be as near perfect as possible. If the hole ends up out of line, the rocker contact will be compromised and rocker and cam wear will result, That's not to say the alignment is always good as original, but this is a good opportunity to improve things.
I have in desperation used JB weld in the holes in an emergency! I smeared a small amount in the holes and let it set, then carefully reamed and "fiddled" the holes to a snug fit. Wouldn't recommend it but it did work and keep things in check. but be prepared to fix it properly sometime ......
Best way to reduce rocker pin wear is to ensure the bushes spin free in the rocker arm. If they are tight, as they are in a lot of narrowcases, then expect excessive spindle wear. I personally ditch the spring on the side of the rocker and shim the rocker for about 4 to 8 thou clearance. Having the rocker forced one way against a shim and the head is not going to help oil flow through the rocker ( to get oil in, it needs to get out!). I never use the rubber in the cover in the race engines (or my road engines) and I don't get any wear to speak of.
Another thing I do which helps is to block the hole in the bevel end of the cam which will force all the oil out onto the oil lobes (what a good idea!), This in turn will throw more oil towards the rockers. Don't worry about the bevels, any oil entering the tunnel area can only escape through the cam bearing and oil drain slot. Once through here there will be plenty of oil in the bevel housing. For further reassurance here, note that many desmo cams are blanked and the Desmo head dosen't have a tunnel around the cam. Therefore the only way a desmo gets lubrication to the bevels is via splash though the cam bearing. One other thing to consider is oil selection as this will also play a part with wear of components subject to high loads like rocker components.
This is just my observations and experience, and I'm not going to claim this will end up with the quietest engine. After all, It is a Ducati and those seeking quiet soul-less engine should look elsewhere
Regards Nigel