I think the first question that comes to mind is, do you have the time/effort available to do your own website and produce the content?
If you've got an idea that is truly not out there, but you think there is a market for it, then with the right webmastering skills, it could be a hit.
But, first you've got to get the site build and then get the marketing started.
There may be thousands of ideas where content is not available yet just because nobody has done anything about it yet or thought of it yet. If it's truly not out there, do you have any idea if people are looking for it? Could you create a demand for it as a niche?
Just as an fyi... UnderwaterDwarfFacials .com is available - it didn't go over as well as I thought it would...
