Always the problem Rob - how do you know if you're buying something worthwhile? I've had particularly bad experiences with bikes "restored" by others, and without being on a rally with a bike, and seeing it perform first hand, I don't know how to assess a bike in terms of value. AT the very least, a close first-hand inspection
From what I can see, the Motomania bike is a very high quality restoration - I doubt I've seen a better-looking CW in terms of its parts and restoration. If its internal condition matches the external, I can understand a higher-than-usual price. It's a very lovely vintage bike, and I'd gladly ride it, or have it in my lounge room.
Re the Tiernan EW, it's pretty tired-looking on the outside, and without some kind of assurance that it's in perfect mechanical condition I'm at a bit of a loss to see why it would have a price tag over GBP10,000. What are those giant wing nuts under the carb and mag controls? Has someone been riding it with a bit of cloth tape for handlebar grips? I'd ride it (if it didn't break down and would go up hills), but I'd never allow it in the lounge room. Nor would I outlay a large amount of money to buy it.
Cheers
Leon