If there's a good 2kgs fleece on a wether, you can sell 20 x 100g packs at, say, £6 a pack? At the moment you would get those prices because of the rarity value, and spinners do like to try a new fluff. But you won't be able to do that year on year.
No reason it wouldn't be good eating. They're large sheep and supposed to be well-fleshed - but that's a lot of money for a butcher's lamb.
So it's the novelty value and something nice to look at and pleasant to be around for the lawnmower. Given what people spend on entertainment for kids' parties, £1000 for a pair of wethers that all your kid's friends will want to come and see (and most of yours too!) is ... still ludicrous.