Agreed. Unless you are making a weapon of a Trooper who has been stranded alone on a hostile planet for the last 20 years... then maybe. Otherwise paint and optional appropriate weathering.If you want a replica of a worn out, beat to Hades E-11 you could leave it like it is, but if you want to replicate a "service" E-11 I would repaint it.
Think about it, if you were a British soldier that was issued that weapon, would you let it get in that poor condition while it was your responsibility to maintain it? The Sergeant Major would flog you no end. If a Stormtrooper allowed his weapon to fall into such disrepair, Darth Vader would probably force choke the poor guy.