Take a look to:
It has been very instructive for me moving the explained scenario to my personal experience.
I'm not a VC but 30% of my time is on presales and techincal proposals. My company works on very challenging and innovative projects on steel-making industry so the problem is staying focused on visionary projects that have an opportunity to be done.
I agree that the trick is:
"As one wise old VC once told me, "the trick in this business is to spend very little time on a lot of deals, and then a lot of time on very few deals." In other words, see everything to be a better investor, but exert a very tough first filter so that you only spend time on very, very few deals. In my experience, a typical VC has the bandwidth to actively "spend time" or actively work on only one to two deals at any given time and perhaps 10-20 in a year -- as compared to those 300-500 they get exposed to."
So the "rule of thumb" should be:
Stay focused on few projects and choose the ones in which in you have more experience. A Visionary Project doesn't mean that you don't know how to approach it but just having the feeling that you can do it...
Visionary means that you have the feeling on how to create value for your customer leveraging your technical experience!