Yep the group books are the WAY TO GO! I love mine.
And it IS worth it.
I was a bit iffy at first on the comic idea, but it grew on me FAST once I realized everyone here was going on with the rest of the story and I was still stuck looking at the Hellmouth Hole In The Ground in a sad and pitiful way.
I have only read the first five, waiting for the next book to come out (more patiently than expected, I should add.)
The Angel ones you should maybe wait for the book too. They seem to be starting out a little sluggishly. I have total faith in them, but it could take 5 for a story to really emerge.