On the JC vs official Chaosium publication debate, I personally judge each book by its own merits. It's not a matter of whether JC stuff is canon or might be supplanted by future Chaosium products. I don't care much about that.
For me, the reason I want more Chaosium Runequest material is because they have the resources to produce the best, most comprehensive material. There are some excellent books in the JC, but there are also some that are...less excellent. And nobody out there is producing stuff on the level of Guide to Glorantha or the upcoming cults books.
It's not an either/or proposition to me. I own most of the JC stuff.