It really depends of the Idea, genuine idea executed well, is priceless, even simple Ideas, but no matter how good your execution of a bad Idea is, well you won't get anything valuable out of it, maybe just loosing time and money, and considering that without Idea, there's no execution, ideas are worth a lot. The problem is: there are not really that much good Ideas as people like to think.

Depends on the idea. The average startup idea is indeed junk.