By that same token, they're not other miners' friends, either. I own three 1070s and a 1060 which I purchased primarily for mining[0] but also because other things I do benefit from the added compute capability. I purchased the first 1070 for less than $350 right after release. I can't find them for less than $400, now.

The funny thing about that is I'm funding my other needs for graphics cards[1] by mining. I wouldn't say I've "paid" $400 for any of them past the first one since all of the others have been funded with mining profits. And I probably wouldn't own three graphics cards were it not for mining.

At some point, I firmly believe, the bubble will pop on all of this and those cards will come back down to earth (I've been saying this for over 4 years, though, and have been wrong for at least that long). Until then, mining to buy video cards is always an option. :)

[0] Mining is kind of a secondary reason. The primary reason is that I wanted to learn CUDA and I know myself well enough to know that if I don't have a project in mind, I will never take the time to learn it, so I set about optimizing an existing CUDA mining implementation and set about learning it successfully.

[1] I play computer games pretty rarely, but I like to fuss around with modeling programs and having a few of these really speeds up rendering in programs that support IRAY. I'm using it for playing with ML code, as well, which wasn't enough of a project to get me interested in learning CUDA, but is enough to keep me interested now that I know the language a bit.

Are people now moving on to nvidia cards for mining? I haven't followed closely for several years, but back in the day, it was all about AMD because nVidia's chips were much less efficient at this type of work.

If nvidia is now in demand for mining, are people going for that because AMD is nowhere to be found and they're just going for the next-best thing, or has nvidia gotten better at this?

They are, on the second hand market.