Removing it will not have any noticable performance gain, neither horsepower, nor mpg. In fact, i think somewhere along the lines somebody had their car dyno'd and it came back with a slight loss of power without the restricter installed.
Removing it will make you car louder under heavy accelertation.
I had mine removed on my 95' Concorde for about 2 years with no problems whatsoever, eventully i removed the entire intake box and went with the spectre intake, which made it much, much, louder.
So, imo, take it out, the car will sound throatier under heavy accelertation, even though there will be little to no power gain.
I removed mine and slapped an intake meant for a civic and my car is loud only when I first start it up. It sounds like a jet fighter when it's warming up but once it's warmed up the whooshing rush of air sound is gone and it sounds deeper under heavy acceleration.
Personally I don't care if it makes the car fast or not! I like the way it looks when I open the hood! That's all that counts!