It's all about fame. even if the project is really bad, and useless; if there is community and a lot of people behind a coin, it'll be listed for sure, because it's a huge load of money to earn, for the exchanges
Check for example dogecoin. 100% useless 100% speculation coin.
You can find it everywhere...
This really puts things into perspective for me. I struggle to understand the altcoin world sometimes (vs. BTC - which makes a lot more sense as an investment) because it seems like such vaporware - but I think you're right! Community demand is a key factor here. Now it seems to me getting listed on a popular exchange would be one of the biggest influences on price - though I haven't yet really studied the correlation in the charts to confirm that.
To what extent do you really think getting listed on a bigger exchange might influence the price if you had to guess? Obviously there is no hard and fast number.. but in terms of gut feel.. most important factor? One of the top 2 or 3 factors to consider (in general)?