I do agree that having good ideas is a skill in its own right. But people with bad ideas are idea guys too! You see them all the time in the indie game development scene in particular. "I need a programmer, and an artist, and a composer, to build this amazing idea for me!", together with an 8 paragraph wall of text (the paragraphs are if you're lucky) describing the idea, and as you'd expect from somebody who couldn't be bothered to develop a single skill, their game ideas are exactly as good as their programming, art, and music.

I find that the strength of people's ideas tends to be highly correlated with their overall skills. I don't know that you can develop the capability for good ideas without getting your hands dirty learning a field, experimenting, absorbing all kinds of information and understanding what really goes into the making of a good idea. In that way, the person with good ideas always ends up being more than just a ideas guy. They don't just have good ideas, they have good ideas and the skills to back them up. Whereas the "ideas guy" label is usually applied to people who have nothing to bring to the table other than their ideas, and wouldn't you know it, they aren't nearly as good as they think they are.