If you ever want or need to hook up the smog pump again, most of the time they sieze up from carbon build up. They are easy to take apart and clean, I've used carb cleaner to clean them out or a good solvent works just as well.
if your not in a place that tests emisions (GOD BLESS TEXAS) id take it all of anyways. you can always reconect it if you are given any trouble, and you may see some imporved performance and milage. just be sure to plug all the old lines good.
I think the only way you'll see any mileage improvement is if you've been driving with it partially seized for a while. They don't draw a whole lot of power to turn.
That being said, if I understand them right, they're only there to put some fresh air into the exhaust to help the catalytic converter do it's job better. If you don't have a cat, it's not doing a thing.