Hi Bob and welcome from north Cumbria

I like your thinking - the old breeds are great and it's fantastic that we have so many dedicated people able to breed, show and sustain the pedigrees, but the breeds will be safer if there is a commercial use for them.
My own favourite example is the Swaledale sheep - she's very much a hill sheep, useless kempy wool, hardly any carcase to speak off, an absolute git to manage (that's the technical term for a hill ewe, I believe

) - but the North Pennines and Weardale is absolutely covered in them as they are the female parent of the North Country Mule, which is still a very sought-after hybrid sheep, being thrifty and hardy (thanks to her mum) and bigger, profligate, milky and with better wool and carcase (thanks to her dad a Blue-faced Leicester.) If there were no market for mules, the Swaledale would nosedive towards becoming a rare breed very quickly.
Someone on here has been pondering crossing a Black Welsh Mountain with a self-shearing type, either Wiltshire Horn or Soay or similar, to get a visually appealing, very tasty, easy care smallholder sheep.
See
http://www.accidentalsmallholder.net/forum/index.php?topic=17585.msg166442#msg166442 for the whole discussion.