I managed to pick up issues 6-19 of Kirby's 70's series. For the most part, I thought it was very good. The first dozen issues are entertaining and interesting, then the series takes a bit of a dip from issues 14-16, then the last few issues are good again until it gets cancelled. It's a shame that Kirby never got to tie up some of the loose ends, though Roy Thomas attempted to in some Thor issues. I think Kirby does present some interesting ideas here, especially the Uni-Mind. I'd say give it a shot.
Now that you mention Kirby's Fourth World, that is something that I've been meaning to read myself.