Removing plastic phase plug from tweeters?

I read somewhere that removing the plastic cover from metal tweeters will clean up the treble and make the speakers sound smoother and more natural. But ive also heard that this "phase plug" or whatever its called is there for a reason- to break up any unwanted resonances that may be caused by a metal tweeter.

Has anyone ever done this, and what sort of results did you get? I'm considering doing this to my PSB's but dont want to kill the resale and possibly make the speakers sound worse.