My father-in-law just paid £5,500 for a late 2011 SE (ETA: it's a CVT) model with 19,000 miles in a private sale so I guess the EX would be worth a little more. I haven't studied Jazz prices but generally one snag with buying the top model is once they get to a few years old all the trim versions are worth similar amounts.
PX value is impossible to say - last time we got a big discount on the new Jazz we were buying but of course that meant they only offered a basic trade price for ours - in fact they used WBAC to value it, then gave is £50 more. I felt a bit insulted by this process, but overall the deal was OK (not great though).