The Maxima's alternator is 90 amps compared to the Z's 70 amps. If you are not running any additional electrical parts you wouldn't benefit much from this but if you are like some of us and have a deck, amp, subwoofers, and more it gives you a little extra power generation to work with.
I would wait and do it next time your alternator gives out on you. Until then I would probably sink the money into something else. In your situation it's not a big deal necessarily but it would be nice to have.
Wait until your current alternator gives out and do it then.