General rule of thumb is that in a 3000 lb car, (we are a couple hundred heavier), you knock off about .1 second in the quarter mile for every 100 lbs. reduction. Think of it the other way, too. Put a 200 lb buddy in the passenger seat in a street race from a dig and you'll be about .2 slower through the equivalent of a quarter mile. These are approximations based on weight to horsepower ratios. The heavier the car to start with, the more weight has to be removed to achieve any benefit.
Trying to get 100 lb weight reduction to drop your quarter mile about one tenth (also about one car length advantage) in the quarter at our weight, is going to be a task in a daily driver. Yeah, you ditch the donut tire and jack, pull out the rear seat and the passenger seat and some of the soundproofing (we ain't got much to begin with) and you'd probably get there -- all for .1 second. Unless you are building a dedicated race car.
Also reducing unsprung weight by using lighter rims, improves (sometimes dramatically) handling on a road course. At the drag strip lighter and smaller diameter rims (rubber is lighter than metal) and lighter rims together with narrower tires on the rear might help too in an all out drag car might help. But FWD cars are not a very wise platform for drag racing anyway.
But just pulling the back seat is not going to do much. Probably not measurable. The concept is valid, OP, but the rear seat ain't nearly enough to matter.