Well you are all such an interesting, informed and articulate lot I thought I would throw in something maybe (

) a little bit contentious.
First let me say that I think it is tragic how many diverse breeds and crossbreeds we have lost in the last fifty years so am very pleased that there are people (like many of you on here) who will help to keep the rare breeds and breeding practices going.
BUT ... to me, there is something not quite right about seeing (for instance) Belted Galloways munching away on ground which is frankly good enough for arable in sunny Wiltshire. To me, the whole point of the Galloway is that it is supremely hardy and thrifty and it should be wandering miles in moorland seeking tussocks of this and hummocks of that to munch.
Of course it is better to have someone keeping a breed alive, even if in an environment not similar to that in which the breed arose, than to let the breed die out.
But, if a significant amount of breeding occurs in such dissimilar environments, then surely the very characteristics which made the breed a success in its home environment in the first place would begin to die away - and we would be left with something that looked like its ancestor but could not perform in its original environment.