Unfortunately this seems to be too simple. The above imbalance figure includes the bonus for the bishop pair which the side with the minors usually enjoys. To remove this effect I repeated the test with positions where the 3 minors did not include the bishop pair.
An additional factor not covered so far is the effect coming from the number of rooks still on the board. In my previous test all starting positions included 2 rook pairs. The theory says that the bonus for the minors should be bigger if the rooks are still on the board. The bonus might be different if some rooks are removed. So I performed several tests to test this hypothesis.
Here are my results
|QRR vs RRBNN|
Queen side scores 43,0% with equal number of pawns
Queen side scores 23,8% with Minors having an extra pawn
Value of Imbalance for Queen side: -0,37 pawns
Queen side scores 50,5% with equal number of pawns
Queen side scores 28,9% with Minors having an extra pawn
Value of Imbalance for Queen side: +0,02 pawns
Queen side scores 70,8% with equal number of pawns
Queen side scores 44,5% with Minors having an extra pawn
Value of Imbalance for Queen side: +0,79 pawns
It seems the number of rooks has huge impact on the value of the imbalance. Its value changes by more than a pawn.
Probably the imbalances of queen and pawns vs a rook and two minors are to hard to be calculated or require a bigger effort. The missing pawns give the side with the minors some development compensation and also half open files, so the value of the imbalance gets polluted with other stuff. So this remains maybe as a future but not immediate exercise.