I have not invested altcoin, yet. But it seems profitable, and fast rising. And I think it is an opportunity for people who said "Am I late for bitcoin". And I haven't got money for big investments or little risk low income investments. But people who has a lot of money and will make big investments should be very careful.
It is mainly the opportunity and I really see what is not there to invest based on what the OP is asking.
Is that not the essence of investing in the first place ? Maybe I should throw the question back to the OP, what is it that you can get from real estate or the stock market that you cannot get from the cryptocurrency market ?
Everybody cannot be doing the same thing, and whichever market, the sole purpose is to make profit and I believe as long as altcoin investors are making their profit, that is the main thing there.