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.

DropBox was an age old idea....The execution is what made its glory