If you got the car you wanted, what someone else got for what price doesn't affect your situation at all, unless you define how happy you are with your product based on what others have or can get that.
I think you are still kind of missing the point here. What others get is mostly irrelevant, at least it is of me. It is the question of maximizing the relative value of my purchase for me. Say, I'm buying an new car around 2017-2018. What time and place would maximize that success for me.
Buying - and therefore the success of buying - is always relative to what is available on the market. While one can say, buy something when it fits your needs, that is only one part of the equation. My needs are not carved in stone. They are relative to what is available on the market and at any given time (or future time), what is available might actually fit my needs better (or worse).
To me, the time of having some latest and greatest (or otherwise fitting) features adds value to the purchase and, similarly, lack of / lessening of such time takes away from the value of that purchase, because buying at some different point of time would have provided me with more time with said features. Missing out on something may mean I will miss out on it for several years, given a purchase like a car. It is not an emotional reaction to say buying a day later would have gotten me a quicker car, if such a thing happens. It is not an emotional thing to state I missed out on AP1 and drove without it for 2.5 years. It is stating facts - from which many reactions, including emotional, can certainly follow... (In that case no emotional things followed, I am happy with the Model S purchase because the aim was to transition to the Model X, but pragmatically it was not the best time to buy - by waiting a bit I would have gotten more car.)
The wish for a customer to optimize their purchase is as understandable as is the wish of the company for them to avoid doing that and instead buying now. But I am a customer in this particular equation and I have my priorities. I understand optimizing this is not always realistic, and never perfect, but in most cases the chances of doing that through information gathering far exceed those with Tesla.
Buy almost any tech product on average and through good due diligence you can optimize a reasonable time that products remains the top dog at least within that brand (or, say, within a price bracket if not talking a top line model), if this is what matters to you. Also you often have some rough idea on how long to wait for the next major iteration to see if such a thing would be around the corner. But with Tesla this is exceptionally difficult - and thus my opinion.
Once you've done your due diligence, and there is a reasonable chance for it with the product, and you still fail or worry about some small niggle - well, then I would say that is an emotional reaction and possibly an unreasonable one. But with Tesla the pace of changes are approaching the point that for me I can not say when that reasonable chance exists.
And it not just the small things as might be with an off-year model-year change traditionally, with Tesla there can be massive change overnight at any given time. Thus I can not really make the due diligence I think would need to make for a pragmatically sound decision that would take into account this... and that's really too bad.
Maybe the most rational solution for you is once you buy something, don't go back to see what is new or how much it costs until you are in fact ready to buy something new?
This is certainly good psychological advice that I have given in the past myself as well. It certainly can be helpful to stop following a product right after you lock yourself in a purchase. It is not a solution to the practical side of the problem, but ignorance being a bliss can certainly help with the emotional part.
That said, I would prefer not to have to do that with a product I like to follow intently. Part of the fun is sharing the experience through information exchange and that naturally includes sharing of information of future things. So, personally, for me the best compromise is a product where there is reasonable chance of planning and timing a purchase right, in pragmatic terms, and in a way that allows me also to enjoy the emotional benefits (including communality).
I am perfectly OK with things improving and others getting better products after me. I do not always have the latest and the greatest of everything, not even of things I find important. But when making that "investment", be it many times a year, annually, or once in several years, most of the time I would prefer to do it at a time that maximizes the feeling that I did it at the Right Time, whatever that means in individual cases.
With Tesla it is terribly hard to predict that Right Time. Obviously my Model X P100D came at a Right Time given all that is better with it and the speed at which Tesla's change (it has many things since discontinued and it cost much less). That will never change even if something new comes soon, so I will be fine with my Model X as a purchase from this perspective. It was IMO a successful buy and, turns out, I bought at the Right Time in the end.
But that's part luck (and part willingness to walk away from one delivery). That luck could have easily been fouled by an interior revision in Q1 or something. I can not honestly say I planned it like this or even could plan it. It is mostly luck, especially given the process started with a 2014 reservation and Q2/2016 order... E.g. had Tesla been faster with my Model X delivery, I would have missed out on P100D (now suspect if upgrades are really available after all for pre-delivery reservations) and AP2...
What I finally received in Q1/2017 was quite a bit different I imagined over the years my Model X would be, yet in reality I still had and still today have no idea when something new will come after it. And that bothers me when thinking about a future purchase. The sheer randomness and possiblity of massive change at random times...
I would prefer there be a reasonable chance of timing a purchase right - relative to both my requirements and what is availabile on the market around the timeframe - and with Tesla it just seems terribly risky. I can not select a rough timeframe when to buy a Tesla, and then through information gathering pinpoint a specific timing with reasonable chance of success. Last year alone is testament to that when one major change after another followed quarter to quarter...
PS> How do you handle investment in stocks or funds, the value roller coaster there is much higher. Most people just don't check daily what their retirement is worth, probably to avoid feeling like you do - "what? the guy who bought shares in the same company/fund as I did 3 months ago got 10% more shares for the same money as I paid?!?!? Not fair! Now I can't sleep. :-("
I'm perfectly fine with stocks. Stock market is like poker. Always a gamble, but you can get better at it. But risks should be relative to rewards. Stocks and poker provide the possibility of massive gains. I even like slot machines, the cost to play is small enough (and wins potentially massive), even though there is no skill involved - call it entertainment.
I would prefer not to gamble on a car purchase. The cost to play is too much and there is no upside to the gamble. And before someone says well there is an upside with a Tesla, I would counter by saying what I've said many times: There is especially no upside after you've bought the first one that takes care of the main benefit (or when large-battery alternatives appear).
In the past, buying a great car from a brand has usually encouraged me to get another. With Tesla it is more like, I got this right, better not risk it again...