i have a schwinn world conversion, i just threw on fat tires (smooth but 38c) for testing out the cross thing. i added a freewheel, and now im running knobbies. its fun.

id ditch your fenders, and add tires like more like the michelin jet, which is smooth, but designed for cross duty. will help smooth out the roads during your commute. id add a freewheel on the other side, something like a 22 tooth. and you can still try the cross trails.

or you can keep the fenders and the fixed, get a cross bike, and do both. more bikes isn't a bad thing, as long as you have the space for them.