...In addition, that hardware is going to be worth only a small fraction of what he paid for it initially by the time it becomes obsolete.
All of our hardware, GPUs included, will be worth only a small fraction of what we initially paid for it by the time it becomes obsolete.
How much do you really believe your video cards will fetch on ebay when they are lost within thousands and thousands of other video cards just like hem for sale by former miners just like you? Have the recent events in the scrypt mining world taught us nothing about the economic laws of supply and demand and how markets function?
A month ago I sold a 6870 I bought over 2 years ago for 25% more than I paid for it in early 2012. In the future, there will always be people looking for video cards at lower prices for gaming. There will never be people wanting to scrypt mine with obsolete equipment that doesn't provide any ROI. So to answer your question, when everyone begins dumping their AMD gpu's, getting 50% of what I paid back is much better than 0 to 10%. Not to mention, I use my 280X for gaming as well, and only have one other card I got practically free. While your argument holds truth to a certain extent, that extent is substantially lower than you are probably aware.