As I started this thread, I'd best update it. Recently (past month) DT-CNS and H-CNS have offered me full breakfast (for 3 even, but with the coffee tax), so I was pretty happy with that (looked like teething issues had been bedded down to allow at least diamonds a full breakie). Last stay at DT-CNS was rubbish as far as the breakfast was concerned. Their coffee machine has broken (not surprising at the amount of use it received) and they've decided not to replace it, so pay the tax or have the muck, and the breakie upgrade fee was back, oh and they changed the breakie times without advising the guests.
I was reasonably happy with sharing my stays in CNS between Hilton and Double Tree, but I'm a bit over the tour group mentality of DT. Time for a change I think. Might have to be ... HI to see if they've improved.