The problem with key influencers is that they can help you get to the top few percent their crowd rather quickly but their requirements and expectations are totally different than those of the rest of your target audience and by leveraging/listening to them too much you hurt the rest of your users.

Still though, when you're fighting for exposure early on, you may not have the luxury of going against the 'tastemakers' for everyone else's good.

Absolutely and I am not saying that going after them isn't the correct strategy sometimes, but you should always be aware of your balance between these two poles.

All I'm trying to convey is that you shouldn't assume that they represent your average customer. Think of the difference between an iPhone and a Treo or BlackBerry, iPhone was made for the general user who never owned a smartphone in his life, the Treos & BlackBerries are designed for the power-user/taste-maker.