After spending years analysing the way I shoot and coming to the conclusion that I very rarely need to make exposures longer than 4 seconds for my work, I bought a Credo 60 knowing it isn't regarded as a good long exposure camera. I use it on my Linhof Techno. True to form, I'm now making many 30 second plus exposures...
I haven't had your length of experience with my back, but I've been extremely impressed with the performance in this exposure range and sense that after the last upgrade noise performace has improved, especially when doing long exposures or when pushing the shadows. I woudn't call it night and day, but certainly better. It could just be wishful thinking related to CMOS envy, but I agree that things seem better.