It’s certainly not true that there is no normal way to invest in Numerai. If you are an accredited investor with sufficient assets, you can invest directly in them.
Purchasing Numeraire is not the same as investing in the fund.
That said, Numeraire may potentially become more valuable over time if the fund is successful and grows larger and available staking payouts increase. But if you’re buying Numeraire without intending to use it in the competition, this is just speculative purchasing similar to purchasing any other cryptocurrency.