i would say performance wise only at high revs... sound yes...
performance wise only at high revs because that the stock intake system has a balanced designed to have optimal performance over the full rev range, dependant on where it is located im assuming the wheel well behind the bumper if it is removed it will then lead to the eninge getting some form of cold air so at higher rpm it may help
sound... well, might be noticable mainly between 3500 to 6krpm i know mine was till i got a SRI now its ten times louder than before
might wana put that post up in the civic 2001+ section??? i would like to know also cause my misses has a FD1
start a new thread perhaps with the title
(Civic FD Resonator Removal - Worth it "yes or no"...)