I invest to the ranked coins but not go for all because I choose the coins only with big potential in the future, so I'd say if I also invest to the non-ranked coins which I research before invest.
Most of the cryptocurrencies I have in my portfolio are the top-rated altcoins (TRON, Stellar, DASH, Litecoin, Ethereum). Meanwhile, it does not mean that I ignore the other alts. I hold Credits, Napoleon X.
Your strategy is right, most of your money should be invested in the coins that have the most confidence of the community, however you should also invest a small part of your capital in coins that are not very well known because you have a chance to multiply your money many times in a relatively short amount of time by investing in those coins and if you happen to lose you are not going to lose a huge amount of money.