There's a nugget of truth in the concept that FSD won't go up in value due to competition, but honestly I'm not convinced that's real. There's not another car out there that has the technology level that Tesla does, and even if so, it's not like you'll dump your current car and bail. So there's also a nugget of truth that as FSD improves over its current incarnation that it can go up in value. All cars with FSD - not just Tesla - would go up in value in the same way. Features add value, and they always have.
I don't necessarily have FOMA but I would like to know what the price is of FSD when it reaches end-state. In my mind an investment of $6k right now, current price, is totally worth it if the end state was, for example $10k. And then kind of a realistic expectation of where my car will be at that point. Could FSD be "real" in 3-5 years? Would I want to "test" the software until then, or would I just want a new car at that point? And honestly that cost might be much greater.
Also, do I really think that FSD features might add significant value until that point arrives? Auto-lane change is neat but largely unneeded. I have Autopilot (autosteer, autospeed, TACC version) and found that my cross country experience was awesome without NoA or lane changes. I just turned off Autopilot and changed lanes and re-engaged. No big deal. But this is just me, and other people might disagree.
These are all personal questions to each reader, but I think more relevant. Prices for features do always tend to go up, but paying for potentially appreciating features on a definitely depreciating body means that the net result might not be worth it.
I'll give it to Elon for pulling the strings of my inner geek though.
Edit: I got to thinking about this a bit more. I honestly don't think that the price of FSD will go up in and of itself, but what we may see is new features added to the FSD package. FSD as-listed right now is a specific feature set. It won't appreciate in cost. What we're being teased with is new functionality that is beyond the FSD package set that is being listed right now, potentially justifying the increase.
It's highly likely if not plausible that the AP+FSD package as it exists today might be completely viable if not lesser cost at some point down the road, but maybe in the 1-2 year future they'll try raising the price by bundling FSD with other features.
No technology fundamentally increases in cost over time unless it is a unicorn, and while Elon might treat it like a unicorn, it's definitely a green banana.