Life's too short Berg, buy one enjoy it and don't worry about the value. Its the enjoyment of the ride not how much its depreciating or increasing. If that was the key concern none of us would buy anything as something more advanced is always just around the corner.
I have a strong emotional bond with both my bikes and genuinely wouldn't sell either even if offered massive amounts over their market value so in answer to your question, on paper my 2013 HP4 Carbon with 17000 miles is probably worth ?15000 or thereabouts but nobody can ever buy it so its kind of irrelevant.
Like all bikes you'll get a better deal coming into winter when people want to sell, buy the best low mileage you can find and enjoy the pants off it.