There are always two ways to look at any opportunity:
1. It can't be done Vs Why it can't be done?
2. It ain't feasible VS What should be done to make it feasible?
3. Value Vs Profitability= How to achieve the critical balance?
4. Approach, just like David vs Goliath. Is it too big to hit or too big to miss?
In my more than a decade of experience I've seen how you approach and react to a given situation determines your future. Act, just not react. Feel free to reach out for any specific input.
I'd encourage you not to look at this as a sole quest. Ideas are easy and have little value until executed. Most creative people are more than willing to share great ideas that they have no intention of executing. The abundance mentality that made them successful also makes them willing to share great ideas. Being around these people either in person, at conferences or even through blogs and videos will expose you to new ideas that have already been thought through and vetted by an expert. As an example Gary Vaynerchuk is always sharing ideas on his videos. Even though millions of people watch it, few probably take action to make it a reality.
Derek Sivers has great insights here on this video https://vimeo.com/26825327
Those who are successful look for a couple of factors:
Is this something that can/will reach the masses? Will the masses "need" this product or service?
Is this product or service something that fills the need for a few, and provides healthy margins, as a result
How soon can I get my investment back, and how much will I earn for my efforts?
Slightly different than ROI; how much work will it take to get this to the masses, or the niche markets, who need this product? How much time and energy will it take to develop/manufacture/market/ship?
I hope this helps, feel free to setup a call if you have a specific idea that you don't feel fits into this metric.