It sounds like you're using your Areas of Focus list more for undefined but specific projects rather than areas of focus.
I use my areas of focus list as sort of a balance checker - mine are things like family, spirituality, career, wellness.
So, for example, maybe one of your areas of focus is the environment, or your budget (I'm not really sure which is your motivation for making your house energy efficient).
A project related to that area of focus is to increase the efficiency of your house. You're right - this is something that you COULD continue doing 'til kingdom come - but you have to have milestones, or it will sit idle or move at a snail's pace. So pick a milestone (also known as "what does success look like?"), and make it your project. Do you want to install CFLs in your whole house? Project. Do you want to get solar panels on your roof? Project. Anything you can't get to right now can go on your someday/maybe. I plan on remodeling my whole house - but right now, all my rooms are on the someday/maybe list, and my living room is the only room I'm working on, so it's on my projects list, and I'm moving forward on it. Once you finish your smaller project, look at your someday maybes and pick the next one that fits with your time/budget/energy/priorities.
It can be hard to pick milestones, so here are some suggestions...
buy food - for me, this would just be a next action in the Errands context "Go to grocery store". I keep my grocery list in the Agendas section, but to each his own
learn to be more productive at work - put a book in your read/review pile and read it, or make a project to take a productivity seminar (including finding one, attending it, reviewing notes, etc)
Get Good at GTD - success might look like doing your weekly review 4 weeks in a row, having read the book through one more time, etc.
Purge Household Junk - this is definitely measurable, and I've done this! Make each room in your house a project. Once you have gotten to the point where you need everything in the room, and nothing else, and the junk is in the garbage or given away, mark it done and move on.
Socializing - having good relationships is an area of focus - not sure you would want to make a project out of it, unless you have a specific goal to reach via socializing, but as long as you have some things on your calendar or you make next actions to get in touch with friends etc, you should be fine.
Get Fit - there are all kinds of metrics you can use here. What does fit look like for you? Does it mean weighing a certain amount? Lifting a certain amount? Running a mile in five minutes? Commit to something, and then schedule in the necessary actions (I know exercising isn't a "have to do on this date" type thing, but for most of us, if we don't schedule it, it won't happen!) Fitness is certainly an area of focus, but you will definitely need some specific projects or it will just never happen. I have a 5K project ending in September.
Take care of teeth - this is an example of something that is not a project, not really a next action, so you will probably do best with reminders. Make a next action to schedule a dentist appointment, but then just put a post it note wherever relevant (probably on the bathroom mirror) to brush your teeth. If you have a mobile phone, you may even want to set an alarm with reminder! The key is to set a system up for yourself that you don't have to spend noggin time on.
Make sense?
