I think in my opinion its not good to stay in one project or altcoin if you want to make a good profit for long term you should try to check the coinmarket cap the top 20 in the list is one of the good choices. you can buy some partial of ethereum and by other altcoin like monero to hold for a long time. .
I think in this matter you have a point, and its a good choice of an idea where the investors can easily pick any of the altcoin. Moreover, you can also invest into potential ICO and you can join too in the signature campaign.