I'd much rather have tatty but original rather than bright and shiny and new looking. Bright and shiny and new looking is great on a new product or one that has been looked after but this loco plainly hasn't been kept in it's a box and has been played with by many people, over many years, and that to me is part of it's charm. I like to imagine all that it has gone through in it's life. Where it picked up this dent and that scratch. How it laid unloved in a box after many years of happy play. Antique dealers call it patina. It's part of it's history and it's appeal.
Of course all this is just my opinion. But then it is my loco. For the time being...
I friend of mine who is into O gauge is going to a Hornby Collectors meeting tonight where he has a friend who specialises in spares. He is going to try and get me a smokebox door. I'd like one from a clockwork model as, like David said, the ones with the big bulb look silly. So much for originality!