SpaceX was valued at about $1.8 trillion upon going public, but its underlying fundamentals didn't justify that valuation. Now that the stock has tumbled, it's time to think about when the right investment point might be. The question now is by how much SpaceX shares might drift lower. First, investors need to realize that SpaceX isn't going to operate like a traditional business going public. Whether it declines enough to reach a $1 trillion valuation -- or about $76.5 per share -- is impossible to know.