[Superturnier]

The most useful MPGuino displays for me are:

-Tank average & trip average. If you can see them both at the same time, you can do your best to improve them during your each trip.
Tank average will be reset during fillup
And Trip average will automatically reset some minutes after the engine has been stopped.

-Fuel used (litres) since fillup or since starting the car.
I started collecting data on my work route. I always drive the same route to work and take notes of the litres always in the same places. I take notes after first 3,6km of city driving, then after a 6,5 km of highway and then after 3,6 of smaller roads. This is a good way to see if your mods will have any effects and you don't need to go for a separate test drive. The more you collect the data, the more it gets accurate.

-Average speed. This is a function I would like to have. Specially when arriving to work after collecting data. The speed has a big effect on your consumption. And when average speed is known then you can see other effects easier.

-Litres/hour. This is sometimes a nice function,as you can see how much your idle consumes fuel.

-Then of course the tank distance and trip distance are good to to have, but I don't need them all the time. And sometimes the Instant L/100km is used, but it will vary every second so much according to your driving, that I would prefer maybe a 10s. average.

As you can see, I try to keep things simple. I have tried to select the most important displays and keep everything else aside.

I like your idea of a vintage FEC. I have a Zemco fuel computer on MyoldFord. It has only one display with 4 digits and it can display speed, distance since last reset, clock, fuel used since last reset and the instant L/100km and a average of L/100km since last reset. I'm quite happy with it. but I have had some problems with the fuel flow measurement accuracy.
The fuel flow sensor has an ball circulating in a track and the fuel flow is calculated from the ball passing through an optical eye
I had a very small leak in my fuel pipe and air was entering to the fuel line. And the mechanical fuel pump created bubbles when hot. The optical eye counted also the bubbles and then the L/100km reading went crazy.
Also I had and fuel filter between the flow sensor and the carburettor. There was an air pocket in the filter and it was acting like a cushion allowing the fuel flow go back and forth with the pumping. Again the L/100km reading went crazy.
Now I have electrical fuel pump and the leak is fixed and the flow sensor is mounted as near the carburettor as possible. Hopefully I can get accurate readings finally. I just need to calibrate the system once again..