Well, potential market is more than just who will buy your product. Recently a very popular show on BBC called the Dragon's Den gave very good information as to how they choose which products they (big, rich, entrepeneurs), would finance, and which they would not.
Basically it came down to the following:
Cost of manufacturing the product versus final price of the product.
Cost of marketing the product to a GENERAL audience versus cost of marketing to a specific group of users.
Ease of production (who wants a product that takes 10,000 steps to make)
Nature of the production (is your product going to contain lead, asbestus, plutonium? You have to be careful with to what you will expose factory workers.
Where will the product be in the next 5 years, and how can it be perfected? In other words, are you about to create a white elephant and something that will be obsolete within a year?
What is the ease of use of your product? Customers want quick and easy.
What is the competitor product that may challenge yours and make you look better or worse.
Therefore, research, research, and research A LOT. There is much more to business ventures than a dream and a vision. That is why 75% of them fail the first year. Just look into what the big guns have done in the past, and follow their example.