It works in exercise, tasking, process, time management and almost every other area of life and it works with MPG/FE too.
That's an excellent point, and a true one. The next question becomes "Am I measuring the right thing? Is there a discrepancy between my metric and the overall goal?"
For example, if you run 5000m and choose (for some stupid reason) to get better at it by sprinting, your sprint time will improve. When it comes time for race day and you run a worse 5000m than before because you gained muscle to help with the sprints, you might cry out "Why? But I was lowering my time/distance figure! I don't understand why I can be faster and yet slower!"
Another example might be sales. Say that you decide that you are making $200/day, and you do that by seeing 10 clients. You figure that if you can slot 15 clients into a single day, you can make $300/day. Instead of working more hours, you decide to rush through your presentation. The end result is that you cram more people in, but none of them want to buy from you because they feel like you are pushy, and you haven't answered their questions because they can't get a word in edgeways.
Instantaneous FE metering is a bit different in that respect, but there are still artifacts associated with improving your FE at any given point in time when your goal is to lower fuel consumption over the distances you need to travel. On balance though, there is no faster learning that will take place as with instantaneous feedback.
Here is my strategy.
Accelarate slow. Get into 5th asap. Do some aero mods, overinflate tires, drive behind trucks on the freeways and streets because they accelarate slow and they drive slower than cars most of the time.
Once I get the hang of the cluch I'll start tinkering with coasting, bumpstartig and etc. I still stall the car.
Compaq, would you at least consider getting a vacuum gauge? If you're hung up on aesthetics you can even stick it in one of those A-pillar pod thingys (to each his own). It's cheap, it won't record trip mileage, but it will help you to manage your right foot. I'm telling you, you have no idea how much a subtle variation in pedal pressure makes until you have a device that shows you the effects in real time.
Now the question, "What good does a vacuum gauge do if it doesn't tell me my MPG?" Well, lots. Manifold vacuum is directly related to instantaneous MPG. Greater vacuum = less air flow into the engine = less fuel burned at that particular moment. This gives you a numerical benchmark for how hard you are accelerating as opposed to the "posterior accelerometer" method, which is notoriously imprecise. In other words, you develop a target number to stay below. It helps on the highway, too. Let's say you're just cruising along at 60mph. It's really easy to apply more pressure to the throttle than necessary, thus burning more fuel than you need to. Call it the "quiet killer" of FE. With a vacuum gauge (or ScanGauge or MID or whatever) you can make a game out of seeing how low you can get that needle and still maintain your target speed.
Use it well and your FE will improve quite dramatically. Vacuum gauges go for, what, $20?