How do you make the case for the unexpected?

My term for well-executed but flavorless, emotionally void, design is ‘cereal box art’. It includes actual cereal box art, architecture, music, dance, video games, movies and anything that has the potential to be daring but takes the frictionless path.

Not every design needs to be an emotionally rich, daring, adventure for the end-user but how do you determine when and where your work can be pushed to challenge expectations?

If you’re working on products for the mainstream this will come up. We all want our products to be wildly successful but that often results in designs and concepts whose edges have been filed away to maximize appeal. Focus testing is great but most of us don't have the budget to collect real data. So, when faced with conservative clients, how do you make the case for the unexpected?