[euromodder]

A lot of these mods have already been proven, and are proven time and again by those who adopt them later on and see their mileage being improved by them.

The open road is NOT a controlled test environment, and environmental factors will always greatly influence your testing.
The effect of small mods will be almost impossible to measure and quantify accurately.

The variations within your A and B tests is bigger than the difference between the averages of A and B.
This can only be statistically significant with many data points.

The gains will however show up in your fuel records over time.
So by all means, add the proven mods, but don't go out specifically to test their effects on fuel efficiency.
A short functional or safety test will do, and if the modification is easily removed, these can even be done by starting off a bit earlier than usual on a planned trip.

The long term, long distance test is the fuel record of your everyday driving.