The previous model of i3-4370, i3-3245, crashed down and depreciated from $129.99 retail to $41 in just 2.5 years, and it expects to reach $25 next year. I'm saving my NIB ASRock B75 for a i3-3245 for $10. Almost there... Time will tell...
Well, yes. It was replaced by newer model with a faster architecture, higher clocks, better efficiency, a far better iGPU, a platform with more features, and so on. Is that in any way surprising? That's how technological advancement works: what's worth $100 in 2011
shouldn't under any circumstance be worth $100 in 2017, as that would imply technological stagnation. While scarcity of replacement parts does some times drive prices up, that's another situation entirely. The reason why AMD chips have held their value better is also in the same ball park: there hasn't been significant improvement per generation, at least not compared to the competition. This all changed with Ryzen, of course, and I'd expect older APU prices to plummet once Raven Ridge is launched.
Oh, and your stance of "saving" a motherboard as "new in box": what's the point? What value does a motherboard have if it isn't used or you have no use for it? I would argue none at all. For now, you're out $84 that you're not getting back, nor getting any value at all from.
Amd as everyone keeps saying: you can get a $40 H110 board and a $60 Pentium G4560, and you'd have a system that would beat your dream Sandy Bridge i3 in pretty much every measure, not to mention have far more modern connectivity, all for $10 more. Why not?