It is amusing to me that companies are hungry for innovation and a stand out new product or service but instead of bringing in someone more likely to offer that up they pick from within the box.
Tom Peters years ago talked about how we need fewer MBAs and to spend more time hanging out with and hiring freaks. Did anyone listen? Not many, or at least few get freaky enough. How do I know? Look at most products, marketing, or even hiring practices. Not just corporate hiring, but startups state they are looking for X number of years of "agency experience". How many rebels, freaks have stayed at an agency for 5-10 years? They've gone off and tried their own thing, changed from one industry to another, failed at something because they dared...
Sure no one wants a freak-for-all! Heck, nothing would get polished up, packaged properly, or shipped on time. Besides there needs to be an agency type to harness the end product to fit within some guidelines. From my observation I would say 2 for every 3 normals is a good mix. And heads-up: they'll most likely expect some freedom around their schedule, pay, working environment, etc.
Ask yourself, do you really want someone who sits at a desk from 9-5 coming up with the next generation of your product? You'll get cubicle, responsible thinking... boring!
Now freak is not a substitute for diversity. There are plenty of shades and sorts that are just different versions of corporate types. It's important to have a good mix of those too; but to avoid a trip to Abilene (the road to groupthink) these should be freaks who would make you uncomfortable enough to know you're out of your comfort zone.
What's your ratio? If your not ready to go full-on-freak, consider contracting a few freaks. Or, at the very least, encourage your current group to get their freak-flag on and create an open environment to allow them space to come play.