Most clutch judder is because the clutch bell overheats, and not because pads get glazed, etc. These bikes were designed for 150-170 lb riders in busy stop and go traffic. Not two up, 400 pounds holding it open for miles. So if you have clutch judder it is because your riding style is harder on the clutch bell than it was designed for. The solution is a better clutch bell.
If your clutch bell is blue, replace it. It no longer evenly dissipates heat. Nothing will get it back to how it was before, and you will spend more time taking it apart when it starts juddering again, than it's worth. Unless your time is worth absolutely nothing, then keep taking it apart and scraping it out every couple of weeks when it starts juddering again. And a bell that judders breaks down the pads faster, so plan on replacing your clutch sooner too.
A very light coating of grease inside the clutch bell can get rid of a lot of noise and judder for a while. It burns off the first time you apply the clutch, but conditions the metal for a while.
Changing to a slightly heavier contra spring also helps. Also, replace the clutch springs with a good set of aftermarket springs. Not the racing ones, but ones that are close to the original. The springs work hard, and after thousands of miles, metal fatigue starts to affect them.
If you replace the bell, one of the new ones with cooling fins will help a lot. Or any top quality name brand aftermarket bell. Most big scooter clutches will outlast the bell, but the bell doesn't look broken, so it doesn't get changed.
If you replace the part that wasn't able to hold up to the way you use the bike with the cheapest one you can find, remember that it was made with the cheapest steel they could find and will start acting up sooner than the OEM one did.
The clutch bell can easily get to 600 degrees or more under hard use. That's a lot of heat.
