There's a guy I know over in England who has a tube frame Buell motorcycle. I believe he looked into the clear coating and came to the same conclusions as you and ended up having his frame nickel coated instead.

I'd suggest getting the frame painted or powdercoated, then detailing around the lugs where the brazing is with a fine brush and contrasting/complimentary paint color. Will give the feel of seeing the brazing but won't have the issues with discoloring. I've seen some really nice detailed lug work.

Edit to add some googled image links:
These sort of show the type of detail paint I'm referring to. A Raleigh I had years ago had a black paint with gold line work on the lugs.

http://apt11.com/wp-content/uploads/...abela_lugs.jpg

http://patentpending.blogs.com/photo...s_bike_021.jpg

http://www.vintage-trek.com/images/trek/TAheadLugs.jpg

http://static.flickr.com/37/81138683_e31c4b664d.jpg