Hi, Barney.
One of the Reference Fours that I picked up at Goodwill had an EMIT-R with an open trace. I used the rear-window defroster repair approach and found it to work well. The repair has held up for a couple of months now. I have no idea how this sort of repair might affect frequency response or other characteristics, but my ears can't tell the difference between this EMIT-R and the original undamaged one in the other speaker.
There is one additional thing you might need to look out for if your tweeter is blown. The Reference Fours, at least, have a thermal switch that's hard wired on the crossover network board to protect the tweeter from excessive current. The switch incorporates a bimetallic strip (see
http://en.wikipedia.org/wiki/Bimetallic_strip) that reacts to heat generated by a small piece of wire that is in line with the positive portion of the circuit that feeds the tweeter. In a typical overload situation, the thermal wire inside the switch should heat up the bimetallic strip and cause the circuit to open and temporarily remove the load on the tweeter. Once the heat diminishes, the bimetallic strip will move back to its original position and restore power to the tweeter.
At some point, the previous owner of my speaker fed so much current to the tweeter that it actually caused the piece of thermal wire in the switch to break (just like a blown fuse would behave). It was necessary for me to repair the thermal switch to get the tweeter working again. I don't know how rare this failure condition is, but I thought I would mention it and perhaps save others a bunch of troubleshooting effort if an EMIT repair initially doesn't seem to work.
Good luck. The sound of these tweeters makes it well worth the effort to perform a relatively simple repair to get them working again.