Re: Why bother?
"In first world countries, buying a refurb phone is still a niche activity"
The number of businesses out there offering screen/battery/case etc. replacement services, as well as ones offering the parts/tools to allow DIY replacement, should be a clear indicator that there's a healthy market for devices which can be easily maintained by their current owners.
So whilst you may be correct to say that *buying* a refurb phone is a niche activity, I suspect that if you also take into account the number of older phones that get passed onto other family members and which will then require the services mentioned above in order to keep them going for a few more years, you'd have a rather different opinion of the whole "design for maintainability" concept - it's not just to allow refurb companies to make some money out of fixing up and reselling older devices...
And when it comes to wearable tech, don't underestimate the desire that some users will have to keep on using a device which they find fits their body really well - things like earbuds are particularly relevant here, as peoples tolerances to what they'll accept having stuck in/around their ears differs considerably, so when you find a set of buds that fits you like a glove then you'll want to stick with them for as long as possible - repairing it as many times as possible to keep it going, rather than just popping down to the local Apple/Samsung/etc store to buy the latest version.