I think you've hit it... the idea + the person. They have to think YOU are competent. Most Geeks/coders appreciate competency above most other traits...

The change-the-world thing... is 50/50, in my experience. Some coders really want to change things for the better, others look no further than the screen...

The last thing I'll say is that it seems that lately... a lot of coders have gotten really judgmental about the DESIGN of the products they work on. So if you commit to having a talented designer contracted it might get you brownie points. Nothing kills the buzz like having to skin one's app with the client's sister's scribblings

please pardon my bluntness

I'd be much more diplomatic (and less honest) if you were my client ;-)