To me good ideas are what I use to convince myself that I have insight into a problem. Its the truth of those ideas (often manifested in particular features) that makes founding a startup seem like a quest for something good. So the idea of someone taking your idea and doing it first, even though they may not have your insight, totally destroys the vision of your company. Its probably a good thing if you release and are copied, they'll always be playing catchup, but to be trumped before releasing...
I think startups who fear investors do so because of the 3 person startup they are imagining the investor shopping their idea to. Its probably not reality, but no one wants someone else telling their story before they can.
No easy answers.
BTW ideas are worthless only if you dont want to allocate a value to them.
http://juwo-works.blogspot.com/2007/05/ideas-are-worthless-w...
I'd love to see but one example of that, actually. IMO larger companies don't execute faster or better. About the only thing they do better is market.