I used to buy them all because I love the background and art, but at £30 a pop I had to call it a day. That money could buy me more Space Wolves. So in future, I'll buy the new Space Marine codex and of course, the Space Wolves one, but that's it.
I think GW are going to miss out in future. Yes they'll make more money on the individual codexes but they'll lose out where people like me used to have a large number of codexes which would make us want to pick up the models of other races or maybe start a new army. Now I only get inspired to buy more minis for my own army, which is preaching to the converted really.