Google at least is a bad option. You won't actually get any value representation, any exposure, due to their extreme market cap.

Most likely close to 0% of the SpaceX ownership stake is represented in Google's stock. Let's assume though for the sake of argument that some large part is, say $1.3 billion of the stake is represented (3% of $44 billion). That's equal to about 1.3% of Google's market cap (~$1t).

Whatever you do never buy a stock on that kind of premise. Risking the other 98.7% of your capital to get a meaningless piece of something else (which is already a big something else at a $44b market cap). If SpaceX doubles in value, you'll never notice it (you put $1,473 into Google, SpaceX doubles, max scenario you might make $20). It may be one of the worst reasons to ever buy a giant like Google. People commonly make this mistake when buying Berkshire Hathaway or certain other conglomerates, thinking they're getting a 1-to-1 direct exposure to the Berkshire portfolio (among their equity holdings, only a few matter at all, as with the Apple holding at $110b). I often see it pitched as a form of bonus diversification. Cash and equity holdings on the balance sheets of public companies are essentially never represented at full value in the market cap. The larger the company and the smaller the asset in question, the more likely it is to have something more toward zero representation.

I don't get the Berkshire Hathaway analogy. If you buy that stock, in what way are you not getting "1-to-1 direct exposure to the Berkshire portfolio"? You're owning the same investments Warren Buffet owns, in the same proportions, to within a rounding error.

It would be a mistake to invest in BH because, say, you're really bullish on Dairy Queen, but that doesn't seem like the mistake you're describing.

Math check -- I think Google's SpaceX ownership stake would be closer to 0.13% of Google's value, not 1.3%. Is that what you meant?