Your bike has lasted to 100,000kms. Are you still on the original cam chain, piston, and valves? I would assume you maintain your bike properly so maybe it is possible to go this long. Curious how long the cam chain can last if you adjust it every so often. How often do you adjust yours? I adjusted mine after the first oil change a month or so ago. I didn't hear any noise or movement in there, so I guess it was pretty close to where it needed to be. I've heard of stories of some people loosening the adjusters and it makes some scary pop sounds in there until it finds it's place. My bike sounds like typical 70's Honda sewing machine; so I'm not too worried if I did that or the valves incorrectly.
Mine has 136.000kms on the odometer (103.000 were by me). Actually the camchain tensioner is the part I dislike most. I don't know about the chain, but the tensioner has been replaced at odo 45.000 and at odo 80.000. My bike has had regular maintenance. Usually I do longer with oil than prescribed. There's no harm in this: I avoid short rides. The OEM airfilter elements practically live forever, as they are not plagued by moisture from a blow-by gassystem like the CB550 models had. Actually I've just replaced the old element, that has been in there for over a decade by a new one achieved from DS for a very reasonable price. I was not surprised I didn't notice any difference between the old and the new one. A lot of nonsense has been posted about paper filter elements. Few people know that paper airfilter elements filter better over time as the trapped particles actually
increase the filtering surface and so increase its capacity. I've learned this from a man who's company sells airfilters! The time it took me to replace the element was less than 15 seconds! Your model has that blowby-gassystem, so routinely inspect your airfilter element for soft wet spots, sometimes they're a bit brown. It would indicate wet crankcase fumes were at it. It goes without saying that even partly wet airfilter elements have less filtering capacity.
In my archives I have an article about a CB500 owner that at that time had already done 225.000km with his.
I don't remember about my pistons - they may well be the original - rings were replaced though. Primary drive chain is still the original. Although I myself took the engine apart, I let a pro do the rebuild as I do not have the tools, let alone the experience to see what is worn and what not. This was decades ago. A few tips. Do the tensioner adjustment by the book (but not by the Owner's Manual!!!) or Bryanj's method. The latter method was practicised by many dealers, but you may need a helper.
As far as the ignition, when you have the original breakerpoints, you can keep them. You could consider a transistor ignition like the one I built myself (a copycat) or have Hondaman's. As far as spark performance, you won't need more
anywhere in the rpm band. If the breakerpoints are aftermarket however, costwise, you may as well opt for a simple EI like Tytronic. As far as your carbs, ride your bike regularly to avoid slow jets becoming partially blocked. You may want to add just a little bit of an additive. Oh... when you make adjustments @ idle, make sure you have a
true 1100 rpm. I once serviced a K3 that showed 1400 on its tacho where my known good digital meter read 1000 rpm. Imagine if I had not noticed this and had tried to find a nice idle at '1000' on the ND tacho. Actually I
did try this and got frustrated. Then I connected my digital meter and the mystery was solved quickly.
