As an attorney, I would answer that a good NDA is invaluable; however, in the world of business, finance, and VCs, asking any potential investor or business partner to sign an NDA right off the bat may leave you without any investors.
Don't give away everything about your plans, but be prepared to be able to pitch your idea with enough detail to make an investor want to know more. You could later ask for the NDA, but in all reality, there are probably many other people before you that have had the same idea. The only reason you haven't already heard about them is either the idea doesn't work or the team failed to properly execute on the idea. Most seasoned investors invest based upon what value you or your team bring to the table and that you can execute on your plan, otherwise what is to stop them or anyone else from doing the same thing whether you tell them about it or not.
Your intellectual properly (trade secrets, patents, patent applications, copyrights) may have some value, so you still need to take steps to protect those assets, but the likelihood of lawsuits over NDAs and stealing of ideas are pretty rare. I think it wason Quora who has said that he has never seen anyone litigating over an NDA in his practice. If the person is or has links to any potential competitor or is someone you are hiring to work with you, get a properly drafted document to protect the company's IP.
Just remember, Execution is the key, not your idea.