I recapped mine (4.2's) with Daytons and might upgrade one of these days. I have not used Bob's crossover kits. I think he has an inductor replacement for the iron core one in the 4.2 IIRC.
I haven't done side by side tests but I can tell you a couple things. When I recapped my Klipsches, which I did a year earlier than the diaphragm upgrade, they did sound a bit better up top. The diaphragms however made a dramatic difference and I don't think it was the relative cost. Other AKers loved them, although, again, no side by side tests. The second thing I would say is that I have a pair of AR9 that I spent more restoring than the total I spent on the Klipsches by quite a bit, and I'm actually not thrilled with their top end. If I had a expectation bias, I would be saying these monsters are the best I've ever heard. But I'd be lying. The 4.2's with RussellC's Class A homebuilt amp is the best I've heard, at least with any of my own equipment.