John McMullins from London Business School has a great model for assessing start up idea. I have used regularly. It's called the 7 domains analysis.
It looks at 3 principle factors: the market (demand), industry (supply) and the team. The idea is that once you have a grasp on these areas, you should have a sense of whether a business plan will work, or where the holes are. They also tend to be the areas that investors look at before they invest.
You could easily line the result up against each other and make a decision that way.