Since it seems so hard to find the argument in the question I posed, let me do the same and present it more clearly:
If the people who bought the GTX 980Ti in mid-2015 for 650-700$ were selling them for 300$ a year later to presumably get a GTX 1080, who's to say that the same thing won't happen with the GTX 1080 Ti and GV104?
It will, that's the nature of technology. New stuff comes out that makes the old stuff less valuable.
And if that happens, how does it reflect on the value of these NVIDIA flagships as a purely monetary investment? If you buy the GTX 1080Ti for 900$ and then find that the same performance can be had a year later in a GTX 1170 at half the price, then does that not make you pause to think whether that money spent was really worth it in the first place?
Monetary investment? This is computer hardware, and it always goes down in value over time.
The answer to your question though really depends on how much you value your gaming. If high end gaming is something you do regularly and you get a lot of joy from your GPU, then paying a premium for the 1080 Ti today will be worth it.
If you don't game much or graphical fidelity/framerate is not that important to you, then why are you even considering a 1080 Ti? Buy a $380 GTX 1070 or a $250 GTX 1060 and be done with it.
If this argument is swept aside using the premise that "GPU product-cycles are like this only" and you have to "pay up to get the best performance at this moment", then why argue about NVIDIA cards costing more after each generation, when it is clear who contributed to the problem in the first place?
Why shouldn't NVIDIA and AMD charge more for more performance?
Ten years ago, wasn't everyone who was a fan of NVIDIA recommending an 8800GT over the 8800GTX for the very same reasons I described in my earlier comments?
Tell me what has changed since then?
IIRC, the performance delta between the 8800GT and 8800GTX was not that large, but the price difference was, so it made little sense -- unless you just had loads of $$ burning a hole in your pocket -- to get the GTX rather than the GT.