First, let me say I think this will have a cult following like the hackable versions of the WRT54, I don't think MOST people want it. That said, I've never experienced this:
> it's pretty beat up. Screen is scratched and dimming, the case is scuffed and creaky, buttons don't quite work, connectors are getting glitchy, the battery is dying and both CPU and memory are getting old.
I've experienced each one of those, but I don't think more than one ever.
My last phone, I bricked the internal storage when it was only a few months old and it wouldn't boot. Its replacement had very similar specs. Had I purchased a camera module, or IR module, etc. I would definitely have reused them. The device before that, the power button broke. The device was still up-to-date enough, it just couldn't be turned on and off. In both instances, the screen and other parts were fine. I don't think I've scratched up a screen since the days of WAP feature phones with plastic screens. Glass is hard to scratch up.
Of course your experience may be different. That's the point, actually, different strokes for different folks
The other category of use-case other than the hacker/maker types may be preconfigured specialized versions from value added resellers. You may have seen firefighters trying out Google Glass. A firefighter phone would have a water resistant case, an IR camera, which is just a regular camera with the IR filter removed, a very loud speaker, a close-proximity findme feature, etc. It could even have a software defined radio module to use as a radio.
Next door to the fire training field is the search and rescue training center, and nearby the paramedic training. Search and rescue professionals might like some of the features of the firefighter phone and buy one configured with search and rescue modules like an upgraded GPS, compass, and a larger antenna for extended range.
Ps - I with the fire instructors and I'm a step ahead on that particular market. There are many other markets, though - extreme sports fanatics, outdoorsmen, MUSIC phones with great speakers ....