As Cribeiro implies this is very subjective, only you can decide for sure. In general, based both on price and quality of sound, most would consider the B&W the better speaker. But the Wharfedale might have some characteristic that appeals to you personally.
Also, you don't mention the
actual price. For the deal to be reasonable, the actual selling price would have to be less than £129, which is the current discount selling price of the Diamond 9.1's.
And you would need to determine the equivalent new price for the B&W. Typically, half to two thirds the original selling price, is about right for speakers in good shape both electrically/acoustically and physically.
If the cabinets are substantially scratched or the cones look weathered and worn, then the price drops below 50% of the original discount selling price.
Right now there is an EBay.Uk action going on for this speaker with the current bid at £52.65 -
http://cgi.ebay.co.uk/Bowers-Wilkins...3286.m14.l1318
I am also aware that at a recent US Forum-For Sale site, they were being offered for $250 (£125) in claimed excellent condition. So that give you a working range of value.
Again, what I would like to know is the original discount selling price, the current selling price, and more details about the condition.
A well cared for speaker should last 20 to 50 years. So age alone is not a problem. I frequently post in other forums where people take pride in the 'vintage' speakers they've gotten a great deal on. So, again, age alone is not a problem. Original price, current condition, current selling price, and the current market for similar speakers is what matters.
If you like them, and the price is right, and they are musically/acoustically in good condition, then go for it.
steve/bluewizard