so interesting follow up. I actually ended up at a dinner with 3 established bloggers tonight. Two didn't have a media kit, one did (the largest of the 3) and said, that if anything, it's important for you to have a media kit so people have some sort of idea where to gauge you, even if they've never heard of you. But it's especially important if you DO have a following that is worth showing to a PR rep. (Guarantee you there are people in this planet, who do not know who Michelle Phan is, but if you list her credentials to anybody, they'll realize that she's gotten to be a pretty big deal, even if they're not familiar with the beauty industry)
It's hard if all you are is a name and a blog, but if you have a well established following, it helps to let people know so they can try to compare it with other facets of advertising that they ARE familiar with, as well as compare with other bloggers who they might be in contact with.
Do you need a media kit to become successful? no.
Can a media kit help you? yes. especially if you have a stronger following than it looks like on the surface.