An assembly gathering several thousand people, optimistically a hundred thousand will have an impact. It will inform world government that the people of the USA are attempting to redress a grievance. Only three percent of the then American population were actively involved in the Revolutionary War. It does not take a majority of free men to cause a revolution it just takes a certain number of Brave men to do this. It will bring to the forefront of international attention a growing issue here in the USA, that of discontent and dissatisfaction. The remainder of world leaders will certainly discuss this among themselves and perhaps pick sides so to say between the Government and the citizens of the USA. There will certainly be interrogatories in certain international leaders circles about "What are you guys going to do about this problem?" Questioning the GOvt. of the USA. I do believe that those responsible think they have gotten away with 911. However my ear is on the ground and I do not believe that to be the case as of yet. There will probably be lots of support from common people from all over the world. In fact covertly US citizens have sent money to revolutionary factions in years past for support, as well as arms and supplies. Like the IRA, Cubans, to name a few.
The attention that I think will be paid is pressure from other world leaders upon the US government.