I understand your points. However, removing the barend weights with the stock grips made no differance in the viberation of the bars on my bike. The viberation was the same at 65mph with or without the weights. When I changed grips the viberation decreased by I would say 30%. After filling the bars it brought the level down another 50% . So, i have an improvment of 80%. I can live with that. You will never completely remove all the viberation out these bikes no matter what you do. But that does not mean you can not try!
Your last post helps fill in the blanks as to why you've seen some benefit from filling the tubes with sillycone; having removed the bar weights more than likely increased the vibrations as those are damping weights that help quell the tendency of tubes to vibrate think wind chimes. So filling the tubes with any material has some effect; some small some larger than others. If you had a way of melting down some lead and pouring the tubes full that would have a very large damping effect over any lighter material.