WA.
There is nothing wrong with the Shorts itself, many of us have started our flying careers on an aircraft which is a joy to hand fly. It does fill a nieche market, but increasingly it does so at a rising cost to the operator.
Many airframes are aproaching their mid life audits which is basically a strip down and rebuild check which for many operators is simply not viable.
Combine that with TAWS and TCAS requirements its sometimes simply not viable to keep these aircraft in the air. Its a shame, but why spend thousands on an ageing aircrat when you can lease an ATR etc with none of these worries.
As far as value ? An aircraft without either of the above is basically worthless apart from the engines, its not like buying a modern aircraft, each aircraft would be valued on how much viable flying life it has in it which is why there are so many lying about waiting to be parted out or sold abroad.