yes indeed, I'm looking at the same option. Though need a new contract!
I've driven a couple of the earlier 530D's, they're comfortable mile-munchers. the heavy lump in front changes the balance a little over benzine powered e60, though still a lovely BMW drive. They certainly pick up when the loud pedal is encouraged. Sadly diesel doesnt seem to be covered in the "so you've bought yourself an e60" pdf.
As Dan mentioned, swirl flaps potentially disastrous - easy and inexpensive delete.
LCI seem to be harder to find, I understand the improved iDrive is favoured, and lower risk of flappage issues.
Options commonly found in NZ include the lighting package, active headlights, active steering, spare wheel, leather interior.
Filters seem more expensive than petrol. Service intervals seem good. So overall, the same e60 areas of concern (water leaks flooding electronics etc - see the "so you've bought yourself an e60" pdf), and as with any BMW, evidence of regular maintenance. Needs good long runs to avoid soot buildups and DPF problems.
There's been a nice e60 530D for sale in CHC for a while, has Dynamic Drive as well (I think similar to the M5)... wonder if that's a maintenace liability with age, or just a seriously cool option to feature in a mile-munching distance car?