Though obviously worthless unless executed, a truly great idea is worth a lot. The point is that there are not that many truly great ideas around.
A valuable patent is an example of something that is a great idea. The most valuable patent, for the anti-cholesterol drug Lipitor, generated $105 billion in revenues.
http://www.pellegrinoandassociates.com/most-valuable-patent-...
Atorvastatin was first synthesized in 1985 by Bruce Roth of Parke-Davis Warner-Lambert Company (now Pfizer). The best selling drug in pharmaceutical history, sales of Lipitor since it was approved in 1996
The Lipitor patent is, in fact, exactly the opposite of what you're trying to convey here. There is zero 'idea' behind Lipitor, just massive amounts of screening.
Clearly the money made from Lipitor required FDA approval, etc, etc, which is the execution. However, without the initial inventive step, which was non-obvious there would have been no patent, and fewer profits to be made.
My other point is that truly good ideas are very rare indeed, an idea whose execution is too difficult does not count as a "good" idea.
To me:
Lowering cholesterol with drugs is an idea. Lipitor is an effective, workable execution of that idea.
Qualifying an idea with "executability" makes it an invention.
I am only using patents to illustrate both that "ideas" are worth something, and also that it is actually very hard to have a truly good and original idea. (The WWW is another example of a great idea) Most people's "great ideas" are really not that great at all.