IMHO you can run it without destroying its value as a collectors piece. That may be less true for the modern museum quality models where getting them on the track and running without a fragile bit getting knocked off is a worry but I do not think light use of the earlier more robust models is a problem. Indeed the ones where people have taken them apart and fitted sound decoders for example often come with a premium on resale. Patina or dirt, its a mystery to simple model fans. But have a wander about Ebay.de to see the prices for used or kept under glass and it does not seem to be a big deal. And you can't easily put a price on the pleasure of those rods whirling with a sensible train of assorted wagons stretching its legs in the garden on a sunny day with friends round.

Graham