The original 'apple' was an idea that many had at the time, two guys with the werewithal to go and execute that idea made it big. I'm sure that in the HCC of the time there were 100's if not 1000's of people that had the idea of a (cheap) computer for everybody.
People that have 'ideas' need to be aware of several really important things:
- everybody has ideas, pretty much all the time
- your idea is most likely not even original ("hey, I thought of that long ago!", yes, so?)
- it might be a great idea but it may never fly, to ask others to risk all to implement your idea for a substantial portion of equity while you risk nothing is out of balance.
- those people that 'had ideas' and made it big invariably were also good at execution.
People that 'just have ideas' usually end up in advertising or marketing where 'brain storm sessions' are their way of minting their idea motor, after all, there you get a salary for just having ideas.
The OP asked if there was room in a startup for an idea guy, the answer is really I don't think so, a startup needs one good idea, then execute it properly the rest is implentation. (Ebay : let's put an auction on the web, YouTube : Let's make it easy to post videos, facebook : let's do 'classmates' but much better). After that the execution takes over, that sort of idea you only need one of to have a viable business.
Sure, during the 'execution' phase you'll need more ideas, but those are usually not going to fundamentally change the nature of the business, unless the original idea wasn't very good...
In an incubator though, there is a place for an idea man. That's where there is added value, also if you're good at ideas you may be good at shooting down other peoples ideas before resources are wasted.