I'm guessing you can over plan some projects, but I'd have a hard time telling what that would look like. What I do know is that I like knowing who is going to do what, and when they are going to do it. I also like throwing my ideas onto paper as fast as possible and then organizing them later. I learned years ago that mind mapping is the best tool for the job. I mind map ideas using only a pen and paper when I am in the field, and I use Mind Manager when I am sitting at my computer or think I might want to share the output with someone else.
Capturing Ideas in a mind map (while using the Mind Manager from Mindjet) is as simple as pressing the insert key and typing. Once I have all or most of the ideas down, I begin organizing them into whatever logical order emerges. This week, my wife wanted to know what we were going to serve our friends at the family cookout. (I think she also wanted to make sure we were going to have something other than just bratwurst as the main dish.) I captured all of the ideas that had come in from friends via emails, added what was missing and was able to present my plan to her for review. Phew, disaster averted.