The time difference will be negligble, unless you're setting yourself up as a 0-60 sprinter on a more regular basis.
I'd forget about the .5 of a second or something that comes from the extra weight. If you get bitten by the weight bug, you end up tearing our comfy trim and "unneeded" panels. It works both ways. It'll only make a difference if you're seriously trying to shave nanoseconds of your 0-60 times.
The weight in this system is not centred over the driving force, i.e. the front-wheels. That said, the increased weight is not spread evenly over the wheels, therefore this will only have a slowing effect. Definitely not a traction-inscreasing one. Fact is, the car will be slightly lower on its arse-end now. Not an ideal situation for an FWD. Nevermind.