How well I know the theme-choosing process! My daughter went through at least seven before we finally settled on "Something Tropical." She kept changing it just as fast as we could find the decorations and band. Finally we had to put our foot down and say this is the FINAL one, choose well! Then again, it is her special day, so we wanted to make sure she got what she wanted. Not *quite* spoiled... we think...
Anyway, what ended up helping the most was, believe it or not, hiring an event planner. My husband and I swore we weren't going to make this into a big production, but one thing led to another, and frankly it's just easier to let someone else handle it. We found a pretty affordable local woman on
http://www.gatheringguide.com/ec/event_planners.html that was able to handle everything, and convince our daughter of a theme! Maybe you can try it.
Best of luck,
Marilyn