> It's probably necessary work, but not important.

I like the direction you're going with this but note that a task being necessary also implies that it is important - otherwise it would be optional!

The only success I've ever had (but at a small co) with getting others to work out what is important and what isn't is by forcing the requester/decision maker to prioritize goals against each other. It gives the opportunity cost a more personal, and therefore real, taste.