I think the proliferation of live CH material was due to the band recording many of their shows themselves. Because they then owned those recordings they were free to do with them as they wished. Luckily for us they made them available.
I would guess that few live Split Enz recordings exist simply because the band didn't make many recordings themselves and the few recordings that do exist tend to be when the band was recorded by a third party (radio/TV etc etc) who owned the recordings. As we've all read, some of these third parties didn't have good archiving practices in the 70's so many of these tapes were lost, damaged or destroyed.
Those that survive, like Camus says, probably need a lot of work. But I would say most of the high quality recordings are/were owned by somebody else and using them (if they still exist) would not only cost a lot of money (making a fan club release prohibitive) but you'd also have to get the band members involved in the recording to agree to a release, and thats a whole other thread . . .