Edit: He responded when I was composing. Sorry to all.
I'm a little curious as well. I can't speak for Jim, but in July he wrote:
Really, there's not much you can do with the standard Bugle to improve it. Aside from a chassis and better connectors, the only improvement would be with C3, C2, C1 locations, and the recommended parta are really quite good. Or you can change opamps. Some people like the OPA2604. You could lose the sockets too.
He didn't address the resistors, but his post implies that maybe there's not much to be gained to tweak beyond the opamps and C-1,2 & 3. But of course, this quote may be out of context here and that was a while back.