Anyway, what really struck me was the trade in price for the old Yaris, which was the same that we paid 4 years ago as the final payment on the PCP, £6,600. So she has effectively had depreciation free motoring for 4 years. Are second hand prices really that high at the moment? (Although I expect my 4 year old Logan is now worth about £2:50).

It is because we are talking about a Yaris hybrid. Despite how some view them, they are an extremely desirable used car, just look at the used prices. Cheapest on Autotrader is a 2013 cat S write-off at £4785, next cheapest is a 2012 eample with 108k miles for £5420. Compare that to a non hybrid (2012 onwards 1.3 petrol) Yaris, the cheapest is a 2013 cat C write-ofor £2690, then a 2012 122k mile car for £2995.

How well any car holds its value is very much dependant on what it is.

Anyway, what really struck me was the trade in price for the old Yaris, which was the same that we paid 4 years ago as the final payment on the PCP, £6,600. So she has effectively had depreciation free motoring for 4 years

Sort of. It must have cost a fair bit during the first three years, and there are sometimes financial/tax avoidance reasons for a good trade in price against a high purchase price, on which you might well have been able to negotiate a reduction if you were a cash buyer with no car to trade in.