I'd agree with Jethro. I think pruning lists is crucial to keeping a GTD system functional. Otherwise, it's impossible to sort out what's important in the moment and what is not.

When I first started GTD, I put everything I wanted to do into my projects and next actions lists. The result was gargantuan, unmanageable lists. Then, thanks to this forum, I started to realize the usefulness of the Someday/Maybe list. If you park less-urgent stuff there, it won't get lost, but it won't overwhelm you every time you look at your lists. This, to my mind, is basically a way to prioritize your actions.

You might consider dividing your Incubate category into two steps, such as "Later" and "Someday/Maybe." The Someday/Maybe list would be more of a wishlist for possible actions. The Later list would be for stuff that you need to do at some point, but not now. To my mind Someday/Maybe sounds too wishy-washy, too hypothetical, too far in the future for all that intermediate stuff (i.e., necessary but not urgent). Thus, it's helpful to have a release valve in your system like "Later," to drain off some of the bloat in your lists. This way you can defer items (with the confidence that they're in your system), but not worry that they'll get lost in the la-la land of Someday/Maybe.