[brucepick]

You didn't say whether you were a parent or grandparent of that baby.

Either way, my guess is that the baby's (other) parent or grandparent will more or less hand you your head on a platter if you do that mod. The mod also reduces the possibility of an adult traveling companion.

In my humble opinion, incrementally gutting a car is a fairly radical path towards fuel economy improvement. There's a lot you can do that will get you more gain than you will get from the removal of the weight of one seat.

Just my two cents of course.