I would say equipment costing of over £20,000 suffers the biggest drop in second hand value. Over and above that the higher you go the bigger the drop.
Equipment is only worth what someone is willing to pay for it, no matter how good it may be, and only a few CCs in the UK would be willing to pay more than £20,000 for a second hand set up.
If you purchased expensive equipment, you don't do so to sell it on after a short period of time, you buy it to use it, in the hope it will pay for itself. It is also nice to have zero tax to pay for a year too.
Dave.