You might also consider repeating your experiment of adding mating
potential to a bishop.
Another consideration: does the value of mating potential depend
significantly on how many other pieces already have it? If you replaced
rooks on both sides with a similarly-valued but non-mating piece, does the
value of commoners relative to knights go up? If you replaced the bishops
on both sides with a similarly-valued piece with mating potential, does it
go down? I think Betza suggested once that it was important for a side to
have a piece with mating potential, but not so important how many pieces
had it.
