In addition there is always the question of livery. There are some beautiful paint jobs out there and some very sombre ones.

Now, that is a very interesting point, caterpillar, even if it was perhaps not quite what you meant! Beauty is in the eye of the beholder, we are told. But what does the eye behold? Does it see the surface, the paint job? Does it see a little deeper & look at the visible lines of engine? Does it see deeper still, and consider what the purpose of the engine was, or whether it was a success or a failure? And is success & failure considered in purely engineering terms, purely financial terms?

Each to their own, I guess. And answers on a postcard, to be dispatched by the next passing steam loco, since no-one's spoken up for the Deltics… ;-)