As someone who has spent too much time and too many resources worrying over vintage cars, I think there are (at least) two components to a used car's value. The first relates to objective performance/reliability characteristics. How big is it? How fast? How efficient? The second relates to what you might call mystique. What does it represent historically? How sexy is it? How does it make me feel when I drive it? How cool is it? Does it dilate my pupils?
My 1979 Porsche 911SC is slower than most new Honda Civics these days and it's not very reliable compared to those Civics. But it remains relatively valuable because of how it performs on point 2. In fact, it'll continue to get worse in relative terms on Point 1, but I think it will never go down in price because it will increase monotonically in terms of Point 2. A new Civic will never be more valuable that it is today unless it happens to be a rare performance model or a museum piece.
On point 1, the original roadster performs pretty well. No gasoline, pretty good range, very good (but no longer world-beating) acceleration, reasonable reliability. It is starting to show it's age relative to newer Teslas and Taycans, and my brother-in-law's new Corvette will beat it in a drag race.
But I think the original roadster won't go down in value because of Point 2. There were very few ever made. It was desirable, sexy, fast, and essentially unobtainable for most people when it was sold new. It has always been an aspirational car. Replacement of a battery is no worse than an engine rebuild in a Ferrari or Porsche. Only George Clooney, Elon Musk, and a few of you on this list were able to buy them new. When you drive one, it feels exotic. The view out the front of the driver's cocoon feels very much like that of a Ferrari or even a GT40 or Porsche 962. The bubble windshield and the flying front fenders just feel different and racy. Hit the throttle and it feels amazing. The Lotus engineering that Tesla tries to downplay can't be hidden: It has magnificent steering feel, it handles very well, and it's softly sprung for a car in this category. Those are all exotic Lotus attributes that some Silicon Valley engineers could not have done themselves. It's made of carbon fiber and the door hinges are milled aluminum. It's as low as a Ferrari or Lambo. People stare at the car. Drive up to a cars and coffee and park next to a Lamborghini, and you get just as many people ooo-ing and ahhh-ing over the Roadster as you do over the Lambo. My 14-year-old son and his friends are more excited by the Roadster than they are by Porsches.
Furthermore, and perhaps most important, this car represents something significant historically. The Porsche 959 and Carrera GT, the McLaren F1, and the Ferrari F40 have shot up in value because they represent something historic and unique: The first AWD supercar, the last analog stickshift supercar, the no-compromises pure expression of the designer's passion, the last car made while Enzo was alive, etc. The Tesla Roadster was the first real electric car, it feels nearly as exotic as a supercar, the company has gone on to significant success, it was launched to Mars! It belongs in a museum. I am happy I got mine when I did. I think it's a good investment in addition to being an engaging automobile.
(it's been a productive Zoom meeting I guess)
and asking prices are up to 150k without the 3.0 upgrade. IMO that's insane! If you add 30k for the upgrade you are only saving 20k vs a new Roadster. 
