If Tesla keeps growing 40% for 10 more years (which would be hugely amazing achievement), in 2030 it will become the biggest car producer in the US, selling something like double the number of the next biggest competitor, GM. I'm not going to speculate on likelihood of this, but consider this: if the optimistic scenario is that future revenues are expected to be twice that of GM, wouldn't you expect Tesla's value to be something like twice of value of GM, additionally discounted by time needed for these revenues to materialize? Alas, the market cap of Tesla is >10x that of GM.
Moreover, the market cap of the biggest car companies have been relatively stable over last 10 years, as the market cap of Tesla was soaring. If the expectation is that the Tesla will eat the automotive market (as it well might), wouldn't you expect the market cap of other companies fall accordingly? As of right now, it seems like the market expects insane increase in revenues of entire industry, not just Tesla, which doesn't seem likely to me: Tesla's growth is almost certainly mostly predicated upon cannibalizing sales of its competitors.
I think Tesla is great company, and I think Elon Musk is exactly the kind of person we need more of, if we want to have bright future instead of stagnation or degeneration. My only point is that Tesla's market cap seems to be greatly inflated, by factor of at least 5x, and possibly even 20x.