There's two things here;
1) Bike condition at high mileage
2) Bike value at high mileage.
Number 1) is easy; if the bike has been serviced properly, cared for and looked after there will be no problem with it at all. Not at all. Modern engines are awesome, and the rest on a bike like this is pretty easy and cheap to service.
Number 2) on the other hand is a bit trickier. When I sold my 2001 GSX-R1000 in 2003 with 24,000 miles on it, it was difficult. The bike was in really good condition, it even had original chain and sprockets on it. Either way, what I was told was something along the lines of. When someone comes to buy a GSX-R1000 of my vintage, there will be a row of them in the showroom. Mine will be priced lowest because it's got most mileage on it. However, there's 8 of them "in front" of my bike with lower mileage, some with mileage so low as 4,000 miles, average around 6,000 miles. The price for these bikes, will be average, with average miles. However, the seller will need (in this example) 8 other buyers before my bike will be sold. Simply because all other bikes are better.
This means that there will probably never be a situation where my bike will be sold because there will always be a nicer GSX-R in the shop. This results in a simple fact; Supply is waaay greater than the demand for my "high" mileage bike. In other words, my bike was close to worthless.
In the end I think I sold my bike for ca £2,000 less than most average prices (and that's a big drop for such a bike).
This story translates to your find in one way: It's overpriced for what it is. Not for what condition it is. You can simply add £100 - £200 and get a bike with less than 10,000 miles on it.... ergo; HAGGLE!