A little sad to see this post end without a problem to the OP's solution. -Because i'm pretty sure that's what the OP ment.
As I understand it, replacing the spark plugs actually solved a problem with an over-eager accelerator pedal, that has now become a lot more civilized.
White Lancer, am I right?

The thing is, my 2004 4.4i has the exact same issue. I have to be extremely gentle on the accelerator to avoid jumping forward, giving everyone else the impression that I stomped the pedal all the way to the floor.
It can be a little embarrasing sometimes. Not to mention quite dangerous in these snowy conditions.

So allow me to repeat the OP's question: Is there any way at all that replacing the spark plugs -and thereby possibly altering the ignition a tiny bit, can have such a drastic -and in this case positive effect on the accelerator's behaviour?

__________________
__________________
2007 E70 4.8i Sport
2004 E53 4.4i Sport - R.I.P.