Hey folks,
here is an advise from a respected Kymco dealer and senior mechanic in Germany who regularily is in contact with Kymco:
He recommends -seriously! - after sanding and cleaning the clutch pads and bell inside, to spray the pads with WD40 Oil. Let it soak in a few minutes and then wipe off the excess oil with a peace of paper towel or similar, so that the pads themselves arent "slippery oily wet" anymore. Do NOT degrease or clean it afterwards! Also give the inside of bell a short thin wipe with these used oily papertowel.
Then reasemble the whole clutch bell belt parts in the right and correct manner.
With this method your clutch judder problems should be solved longterm and you should have a buttery smooth operating clutch.
I know that this method may sound wierd a bit for many of us, yes it does, but this mechanic and several people in the german Kymco forum have used this method and have confirmed, that this method does the trick.
I myself haven´t tested it yet and lived with the judder for almost 20.000km now. My judder issue varies depending on temperature. To cold isnt good and too hot isnt good.
I have planned to replace my whole drivetrain wear parts next year at roundabout 22.000km. Then I will either use a better aftermarket clutch or I will also use the trick with WD40 decribed above.
So, who is willing try it and report in the US?
Stig? Long boring winter days and nights are ahead of us all and your Like for sure estimates some cosy treatment from you. 
Thanks for some very interesting comments.
My scooter's clutch did not judder, but during the previous weekend I removed the variator and clutch assembly on my scooter just for inspection, and eventually discovered some interesting observations and results - which might be applicable to this topic.
I couldn't find any wear on the variator components - everything was clean an I just put everything back in place as is.
At the variator I discovered that the needle bearing was running almost dry - so I removed the old grease and re-packed the bearing with CV joint grease.
Probably the most important observation (as far as this topic is concerned) is that I discovered quite a lot of clutch pad dust inside the bell, as well all over the inner clutch components. In fact - after the clutch bell was removed I turned it over to see If I could see any wear at the inside of the outer rim. The outer rim was still in perfect condition, but probably the most important observation was that I discovered a "puddle" of loose clutch pad dust lying at the bottom of the outer rim.
Gravity obviously caused the loose dust to gather at the bottom of the bell when I turned the bell over.
So I just removed the clutch dust inside the bell, and used an air gun to blow out all the dust at the inner clutch components. I then put everything back in place, and the scoot was ready to go again.
Believe it or not, after this service I immediately experienced an improvement in the scooter's general performance. For example - I use this scooter for commuting on a daily basis - and suddenly I sensed more "power" when I ride uphill on a certain stretch on my way to town. I initially thought it was just my imagination, but then realized the scooter is reaching a higher speed than before when I get to the top of the hill. Unlike before, the scooter is now even capable of picking up some slight speed while I'm riding uphill.
This improvement in performance initially really boggled my mind, because I didn't touch the engine. All I actually did was to re- grease the needle bearing, and to remove all clutch dust inside the clutch bell, and clutch components.
Long story - but right or wrong, I don't think re-greasing the needle bearing caused any improvement in my scooter's performance. I am quite convinced that that the clutch pad dust which gathers inside the clutch assembly by time actually gets trapped between the bell and pads whenever the clutch engages, and when this happens the clutch can easily start slipping.
In short - after reading your comments, I started Googling about cooling bells and discovered some very interesting images. I like the bells with the fins on the outer ring, but thinking back about my experience, I think the bells with fins at the sides, or modifications at the holes at sides is a better idea for a simple reason : the fins at the sides will not only help to cool down the bell, it will also help blowing out the clutch dust which can easily cause improper clutch engagement.
Some pictures of cooling clutch bells which I think might be a better option. I think the bell at the 3rd picture might cause more wear on the pads, but at least the dust which gathers inside the bell will escape through the holes:
