A) Definitely upgrade AKL-DXB* it makes so much difference from J. The daytime flight to CDG may be ok in J.

B) Only if you upgrade DXB-CDG or AKL-CDG. IMO the F lounge is not worth it for that short transit period, will probably get about an hour real time there.

C) I would never exchange miles for gift cards. Worst value ever.

D) In my view, and seat wise EK's J on the A380 is closer to premium economy than to F. I find it cramped. And the service is typically slow with a full cabin. I would upgrade to F on the longer sector in in a heartbeat. F has a lot more shoulder and elbow space, signifcantly wider seat when fully reclined. Plenty of storage space.

*Upgrading both legs is the better value as it will cost 70k miles and is def worth it, so if somehow you could get the additional Skywards miles perhaps through AMEX NZ (20k AMEX MR points) that would be ideal. Otherwise ~400USD is a small price to pay for the upgrade.