If I were to trade cryptocurrencies for a living, I'd invest in so-called "promising" altcoins only for short term and would close all positions after certain amount of time, regardless of the price, because in my mind any new alt is just a pump and dump / ICO scam, and in the long run there will be no fundamentals to support the price - promises of revolution, disruption and so on only can get the price so far, sooner or later everyone realizes that no real progress is being made.
That's the sad truth. Diversification is a good strategy but people forget that Bitcoin itself represents financial diversification. The destiny of cryptocurrency will hinge solely on the fate of Bitcoin for the foreseeable future, so all in on Bitcoin is the way to go as a diversification into crypto.
It's consistently the best performer, and the least affected in bear markets like now. Any gamble on alts, as you say, is short term. You are as likely to lose as to win. Alt speculation is just that, speculation. I see I'm not the only one who sees new alts as ultimately that alone.