I too use expired inks and printheads on teh z3200. I have had issues with the Gloss Enhancer, but, this maybe more to not using that inktank than it is with it being expired. I also think it maybe something electrical as someone pointed out in some other thread. So from time to time I have to take out the GE that maybe half or so full and replace it.
All in all, I would say maybe 10% of some issues MAYBE linked to old ink. I think shaking them is not such a bad idea before doing a set of prints. As Canon does an agitation cycle when not printed in some set time. So, it cant hurt. I wonder it removing a ink wakes the printer up. If not, best time to do it.
I have had my Z3200 for a a long time, but I am not a print house, and I have only ran maybe 1000 prints through it total? So, I intend to keep it ..and I plan to finally start making prints for sale....Last 2 times I got all things ready to go the printer had some failure...LOL. I have learned a lot, and one of those key things is that specific printers work well with a select number of papers, and when you find those, it is a good idea to stay with those papers. Otherwise consider it mostly experimentation and prepare for hiccups.