Hopefully, the bigger names will be on hand to help out when they can.
Even if you can't get known names to speak, always have something fun/interesting for the people to do. Don't make it just all speakers, all day.
Think outside the box here. i.e. Have some kind of "Know Your Constitution " or, "Is this legislation Constitutional?" type of game. Offer prizes (gas/grocery coupons/other things). Teach people while informing them of what D.C. is up to, and why we must hold our politicians to these principals.
Hold the event in an interesting place. (The Reagan Library comes to mind for Ca or possibly have something at the county fairs? Maybe having something in a big park? (fill in your ideas____________).
Consider having something for the kiddies to do. I.e. It doesn't cost that much to rent a bounce house (just make sure you tie it down if it's windy, or might become windy).
You could have face painters, or maybe just have some kind of activities, games, planned for kids.
I say this because so many are working longer hours in today's wonderful(/s) economy, and babysitters can be a luxury they may not be able to afford.
People's time and money are at a premium. Keep this in mind when planning.
IMHO It's best to aim for holding family friendly events that are both informative and fun.
You could start with an outreach to the local churches in your areas.
Another important point is to watch out that events are not overlapping.
If you have 2,3, or more separate people planning something, and they live in close proximity to each other-they should get together and combine their plans into one single event. Chances for a big turn out increase this way.
Take as much time as you need to plan (even if this takes more than a month.)
The more time you spend on planning what your event will be , what message are you trying to get across? how will you present it ? exc... the better.
Also DON'T FORGET TO TAKE VIDEO/PHOTO'S to share with everyone.
Just my 2 cents.
Those are some good ideas, thanks for your input.