What a great topic. I am constantly referring people, and although I used to have a trial and error approach, I have, like you, developed, over time some base rules. For me, one of the breakthrough points I learned years ago is that referrals do not need to be reciprocated directly or at all. They are often like "gifts" (just take it, say thank you, and do good work). The reason is that often people have their own motives for referring you, and that motive does not involve you.
That point works both ways--don't always expect something back. If you do expect something, be very clear from the outset what that reciprocation might be.
Certain people--because of their professional role or their personal make up--are simply not the kind that refer. We need to respect that, I think. Some people don't feel comfortable or want to be responsible.
But for the rest of us who want to help, throughtful referrals can raise your profile, create business for a client and even help you make a few good friends.

