But the Top 2 pages on CMC contain good Altcoins which are worth some attention
Agree. Which is why, you should look for altcoins that are prominent in development and innovation. Additionally, cryptocurrencies that are widely adopted by the mainstream world tend to become successful over time. Personally, I would not recommend the top 2 pages on CMC because there are some altcoins which are not worth the investment nowadays. Instead, investing within the top 10 cryptocurrencies on CMC would give an edge as they're extremely active in the mainstream world.
Altcoins such as Ethereum, NEM, NEO, Dash, Litecoin, and Monero are extremely useful for the world. They're not purely speculative like Dogecoin which had been abandoned by its devs for a long time ago. Instead, some of these coins provide smart contracts, others provide privacy features, while others provide instant and cheap transactions. All of these features prove to be useful for the world, giving said cryptocurrencies an advantage over others.
Still, the driving factor of an altcoin's success is if the same is adopted by the mainstream world. If it lacks adoption, then it won't be going anywhere.
Nonetheless, some altcoins are useless while others are not. You just need to find which ones are suitable for your daily needs. Just my thoughts