If one creates an altcoin today, what are the 3 most important factors that would make it valuable? Or 3 activities that would do so?
The community trumps everything.
Look at Doge - it was created as a joke, it was designed to be the opposite of Bitcoin. So it had very high inflation initially, it had infinite coins, it was designed to be mined on laptops, each coin was meant to be worth only a few satoshi, and so on.
But it's still there, it is still used, it has good merchant adoption, thanks to it's crazy community.