There is no market for ideas for the simple reason that I have to tell you the idea before you can decide to buy it. But once you know the idea I no longer have anything to sell you. If I tell you my amazing idea right now and you decide it is good and go ahead to develop it. Well, you no longer need me and I cannot sue you for not paying for the idea. Not to mention that execution is just as important, probably more so, than the quality of the idea.