I think it has to happen naturally, what percentage of UK Vees' owners are on here? I can't imagine it's that high.
The TVR guys managed it with the Sagaris as most of the owners were on a forum afaik. Now with the demise of TVR, and the fact it's a British car has made values of nearly all of them to creep up.
I think V6s will go up eventually, but at the minute I imagine most people with £20k in their pocket for a toy on the side would choose a Cayman or similar. I know a lot of my friends love my car, but would spend their money elsewhere, either a faster sports car (one is getting a Z4MC) or one with a better badge image (boxster, TT)
Also, isn't there about 280 Ph2 in the country still? Think of Turbo 1/2 values, they're much higher but I bet there are only tens of them here. Supply demand thing