It's a problem of incentives. When I worked in a corporate environment, I worked very hard to ensure that people asking for things were the ones who paid for it -- even internally. A project # to bill against for everything.

In the agency world (where I was), carefully billing time was de rigueur for client-facing people. I pushed to have it apply for non-billable internal people too.

So the "idea people" had to do cost-benefit. Requires a cultural change (and trust), but it brings discipline to both sides. Really helped.