There really was no alternative except to go talk to the neighbor. I would pitch it as something that would be mutually beneficial - it would let more light into his backyard as well.
It turned out he was a really reasonable guy. He agreed that it'd be nice to bring down most of the stuff, and even volunteered his son to do the work.
I noticed a lot of metal art stuff around, and asked what he did. It turns out he's an actual professional artist by the name of Paul Sorey. If you get around the Seattle area, you'll have seen it.
Check out his website at http://paulsorey.com - there's some really neat stuff there.
AND - he's a very reasonable guy!