I do believe it is very important like in any business.

There are numerous success stories from ICO's due to the fact they threw a lot of money into marketing, you are best looking into projects rather than the first one that appears in a banner.

One ICO i am really liking is Crowdholding for example, I haven't seen too much about them, but they are trucking along very nicely

https://ico.crowdholding.com