All Musk's valuations are based on his visions for what could be. It's just that for SpaceX, unlike for X and Tesla, "what could be" still seems plausible.

For Tesla… there is the argument that while "what could be" is very unlikely, if he pulls it off then it is also very valuable. But I not only don't think he can pull it off at all, even if he could don't think he will have market dominance sufficient to justify the price.

SpaceX… may have similar risks, depending IMO more on Chinese companies thinking "Great idea, let's do that but better" than e.g. European companies doing that. But even with that, 27x for current launches, and an additional 3x combined with that for other constellations plausibly gets them to around x80 even if Starship continues to not be reusable.

Starship is a big question mark for me. Assume it works: Would it be cheap enough to induce demand? Dunno. Not implausible, but I really don't know, and that is needed to get up to 700x.