Here's the downside I can see: we're already hardwired to be attracted to things that are bad for us (or for society, or both). Things like sweets; addictive drugs like opiates, painkillers, sleep medications, crack; even underage sex partners. Making it even easier for marketers to appeal to our natural (including our baser) instincts could well push us even harder towards things people want to sell us even though we ought not to have them or do them.
The upside? Positive goals could be aimed at in the same way: for example, getting people to eat healthy foods that they normally would find less appealing than unhealthy ones, or designing an energy-efficient light source with a "warmer," more pleasant color.
The possibilities are almost as myriad as the neurons in our brains. The question is, how much more manipulation do we want to accept?