I had a similar problem but am dealing with it with an opposite strategy--I'm treating OmniFocus as my immediate, always-there tool, and whatever isn't compatible with that (including, whatever is making it too cluttered) lives elsewhere, as project support material. OmniFocus is handy on my computer and my iPad and my phone, so it gets the "immediate" role.
So those errands and single actions are absolutely in OmniFocus. Big projects--and the definition of "big" is getting smaller and smaller--live elsewhere, such as OmniOutliner, sometimes with thin little references in OmniFocus.
I'm going to ramble on, because I like thinking through this stuff, and who knows, it could be useful for discussion.
Let's say that I have a project "revamp wardrobe". I create it in OmniFocus but I realize fairly promptly that it's too big to be a project--this isn't about getting skirts with the new hemline, but about changing my whole way of dressing and thinking of myself visually.
So I perform the process of moving a too-big item out:
- If it seems to be area of focus sized, and I've decided that it does for now, I give it an area of focus folder. If it fits in another area of focus, I'll move it there and I may rename that area of focus. (Example later.)
- I give that folder the standard single action lists that I usually give to areas of focus: Thoughts, Single Actions, Support Material, and (for some areas of focus) Wanna Buy.
- I move all of the stuff that I've been entering for Wardrobe into an OmniOutliner outline file. That stuff no longer needs to be actionable, so I structure the file however I darn well please--or I might have many files, or I might use another tool entirely.
- I link that OmniOutliner file (or whatever I used) into the Suport Material Single Action List for the Area of Focus, so I can easily open it from OmniFocus. It would be less cluttery to put that in the note for the folder, but for some reason I always forget it's there.
Now I have a structure for this area of focus in OmniFocus, but the non-actionable stuff is elsewhere. As time rolls along, OmniFocus will feed the support material, and the support material will feed OmniFocus.
For example:
- I might create an OmniFocus project "Catalog existing wardrobe", which drives me to catalog my wardrobe into the OmniOutliner file, and might also produce a variety of ideas and thoughts about my wardrobe. I do the project, I put the thoughts into the OmniOutliner file, and then the OmniFocus project goes away.
- When brainstorming in the OmniOutliner file, I may conclude that, oh, I really do need that wide black dress belt that I've been wanting forever, and it's time to actually do something about it. So I create an OmniFocus project for finding and buying the belt.
- And I might be out and about and be inspired with some wardrobe-related idea. I enter it into "Wardrobe Thoughts" in OmniFocus on my phone and in my weekly review I transfer those thoughts to OmniOutliner--unless some of them are immediately actionable, in which case I move them where they belong in OmniFocus.
The idea is that OmniFocus is a temporary home for active items, but it shouldn't keep growing and growing--items should flow in, be worked, and flow back out. It's OK to use it for brainstorming but it should, again, be only a temporary home for the products of that brainstorming. It's the support material that grows and grows.
So, at some point I realize that my wardrobe area of focus is producing thoughts about hair, and whether I should explore that weird "makeup" thing they talk about, or at least do something so that my face no longer threatens to fall off in midwinter, and is it time to finally break down and get my ears pierced? That creates some OmniFocus clutter, it becomes apparent that it's time to move that clutter out, and I conclude that my "Wardrobe" area of focus is more appropriately a "Girliness" area of focus. So the existing area of focus changes its name, absorbing a potentially wider variety of actions without adding any more structural clutter.
Then I consider whether my new gym membership qualifies as "girliness", and decide that, no, I don't want my health to be about appearance and self-image, so I create a Health area of focus. And all my thoughts about diet and exercise go into a linked OmniOutliner file, and OmniFocus gets specific projects like, "Find an organic whole-grain bread that I don't hate." Things that I ought to ask my doctor go into the OmniOutliner file, while OmniFocus just has a tickler for "Have annual physical" with a note that reminds me to check that Ask the Doctor list. And so on. Everything that can possibly be removed from OmniFocus, is removed.