I checked my car, and yeah, I just used the original holes to remount my number plate. Pretty sure taken the holder off was just a matter of a couple of screws too.

I just dropped in a K&N filter a few months ago. Made a big difference, especially in the top end. I replaced my spark plugs and leads at the same time with NGK Iridium's. Made a big difference in responce, felt a lot better.

I don't think its worth removing the resonator. I did on mine, but I wouldn't bother doing it again. To get to it out (If I can remember correctly, I did it years ago), just remove the airbox out of the way, should be just a couple of bolts, then there will be some more bolts holding the resonator in, just remove them and it should come out.