HQ should buy the permit and see whatever else is needed. Grassroots efforts don't offer legitimacy for a lot of people. If the campaign puts a hand in this it'll be more successful. Grassroots does wonders getting other people to come and showing up itself, but when it comes down to it, do you follow Ron Paul or his supporter? For a lot of people who don't spend as much time in the grassroots as we do, it's the former.
The point is that neither entity can do it alone as well as the two could work together. The HQ will be great for getting RP supporters out. The grassroots will be good at getting say, Obama supporters involved, as an anti-war rally, and Huckabee supporters involved as a pro-conservative rally. The more people we get the more legit the march is.
As for your second point, I admit that I have very little faith in the ability of people. But let it be known that I hold Ron Paul people in high esteem over the rest of the people.