my first question is, why are Texels so expensive and are they really worth the money?
Supermarkets pay extra for lambs with the size, leanness and conformation they want. It can make £3 to £5 per lamb difference.
Butchers will only buy lambs of the size, leanness and conformation they want.
A tup can sire several hundred lambs a year, and can work for several years. If a tup can add £3 per lamb you can see why a farmer would pay several hundred pounds more for a good tup than an average one.
Plus, and probably way more important to farmers, the price you get for your lambs is a reflection of how good a farmer you are. If you buy better tups you should be producing better lambs that will fetch more money and tell you and your neighbours that you are doing a good job and producing what the market wants to buy.
As to why supermarkets and butchers want the lambs just that way - get yourself along to North Sheep or South Sheep or Scots Sheep and see the EBLEX butchering demonstration. It costs a butcher far more in terms of time and wasted (trimmed) meat (and fat) to butcher a poor lamb than a good lamb, and the best lambs can render more of the very best and most expensive cuts. Once you've seen that demonstration your only question is why they pay only £3-£5 more for the best lambs...