The Gamma500 is an awesome beast, but it has one seriously viscious power band step.
Yes it's flickable, but compared to todays 600 sportsbikes feels like a plank.
Appreciating classic? Definately, especially in a country where Strokers are now banned from being sold.
Fun to ride? If you enjoy adrenaline hits and the occasional trip to the bathroom to scrape your shorts then yes.
Worth it? Depends how much he wants for it.
Here they go for up to £25,000 for a pristine low miler (below 1000 miles)
Personally I wouldn't pay that for one motorcycle.
I could get a C14 AND a ZX14 for that.