I do plan on weathering my rolling stock and loco's. I've yet to see a shiney new piece of rolling stock ever being pulled by a loco sparkling in the sun.
They all seem to have fading paint, dirt and grime in varying degrees.
As for graffiti, unfortunately it's a fact of life. There's a yard right beside Rt 95 at the Providence/Pawtucket line. Must be 100+ cars there. You'd be hard pressed to find 10 without any graffiti, if you could find that many!