Ideas = Novelty + Utility.  

I am not sure who said it but as a definition of "creative ideas" I like this.

In some ways it sums up lots of the problems of coming up with great ideas. Creative people tend to obsess over novelty, businesses tend to obsess over utility. What everyone should really be aiming for is both.

But novelty is high risk. Many successful businesses have been born out of improving on an existing idea, letting someone else take the risk and create the market. The same is true of advertising: novelty is often seen as risky and so 'me-too' advertising becomes the norm.

Agencies tend to like Clients who appreciate novelty. Clients certainly appreciate agencies who get utility.

The answer would seem simple: aim for both