I can't speak to digital SLRs or Nikon digi-cams, but will offer my observations on using an "antique" digital "brick" - Canon G-1 Powershot, mighty with its 3.1 MP resolution. Power-zoom, auto-focus (but non-interchangeable) lens, full manual functions, if desired. Cost me all of $15 at an antique co-op in 2010.
This little beast ( about the size and heft of an Argus C-3 ), supposedly listed for nearly $1,000 at its introduction.
It records on a Compact Flash card, and uses a replaceable ( but proprietary ) Li Ion battery.
So far, I 've bought one CF card, and three generic replacement batteries (one of which failed in six months, but that's not Canon's fault).
Old-age issues I'm gradually encountering:
1) View-screen: which can fold-out / tilt / swing: getting dodgy - no longer works when folded flat against the camera body, so have to shoot with it flipped-out like a flag, if I want to review as I go.
2) Body screws - seems to be shedding them here and there, now and then.
3) Access doors / micro switches - the micro switches associated with the battery compartment door and the CF card door seem to be getting wonky - sometimes the mere pressure of my grip in the area of a door when shooting one-handed or manipulating the camera is enough to cause an issue, and a gremlin shuts-down the camera.
3) Motorized stuff: when the camera is switched on/off, a motor-drive racks the lens out / in accordingly, plus the focus and zoom functions. This too is becoming dodgy.
The optics though, are quite good, and I have shot thousands of images with this "primitive", 10+ year-old digi-cam.
I will eventually have to replace it for two main reasons:
1) wear & tear
2) No longer meets my photographic needs.
I think the lifespan of such devices is functionally limited by:
1) electronics - a friend who has been a career electrical engineer for a major defence contractor attests to the "Tin-whisker" issue of lead-free solders, though that's not the only issue :/
2) construction details / materials -
3) technological advancements rendering the existing models obsolete / inadequate
4) Repair support.
Just some of my musings... I sort of dread replacing my G-1; yeah, it's a clumsy brick, but I know it well; I dread learning ( and paying for ) a new camera / system... especially one that I might not be able to hand-down to succeeding generations as a functional bit of gear...
Regards,
Luddite Frank