[jasong]

With your current setup, you'll find yourself fighting against OmniFocus on a semi-regular basis and you'll probably grow even more frustrated with it.

Why not have two levels of folders?

Also, if you use projects as projects, rather than action groups as projects, you don't have to delete completed projects, you just need to view only your "active" projects. This hides completed projects from view, but keeps them available for historical purposes.

Finally, I don't "forget about" my projects because I don't spend much time in the projects pane; I don't spend much time in the projects pane because I spend most of my time in Context mode. That's where I complete my actions. If I need to do any planning on a project, then I bounce to Planning mode. I also have perspectives set up to handle my project reviews, which, while in Project mode doesn't use the project pane.