Look at it this way. Everything year on year goes up in price. Including snap on tool boxes. If you buy a decent one and look after it then it will hold its value very well as the new equivalent box prices will be going up every year and that is ultimately what they are compared against.
Buy a £150 halfrauds or Sealey set and it'll be worth FA let's face it. But a quality Snap On box should hold value very well and be a good investment.
Your missing the point completely. It's only worth anything if you intend to sell it.
I Look at depreciation when buying a car as from the moment I buy it I intend to sell it. Its literally the only thing I intend to sell.
Maybe for a few professionals that intend to sell up when they are done then resale value might matter. But the vast majority on here will keep their tool box until they are in a box them selves.
likewise whilst the snapon is worth more if you where to sell it, does it really matter if the depreciation on it is greater than the purchase price of the Halfords.
I fully understand if you want a snapon box and it makes you happy then fair enough, that is perfectly ok. But you can't pretend for a second that it's a financial decision.