Unless you’re designing a video game, consistency matters. Not to make things dull, but to keep attention focused on the good stuff. It’s like driving: Because every stop sign looks alike, you can get where you’re going and carry on a good conversation while you get there. If, instead, all stop signs looked different — like, whatever; you know, creative — you’d spend the whole drive worried about whether you should stop, or where, or when, or how, trying to figure things out. You’d lose your good conversation and your peace, and it would be scary besides. That’s what consistency in design is about. Get the routine, navigational stuff consistent so your audience can settle in, then you can have fun with the real stuff.