It is slower to rev up in neutral and then to drop the revs when the pedal is released. My former maxima se (97) and 350z (2001) were much quicker on the up and down -- felt like a quicker-reving engine. Do I have a much heavier flywheel perhaps?

 

Probably because the 3.7L is a bigger engine. But it packs more wallop than the engine on your maxima.

 

I'm more interested in hearing about his 2001 370Z,

 

haha you know what I mean. Was just reading about a 370 elsewhere.

 

oh yes it does.

 

I noticed the same thing. I am sure it's not an issue but some explanation would be great!

 

Could be flywheel, but more likely is the electronic throttle programming and EPA requirements.
Throttle "chops" can dump more unburned fuel into the atmosphere, so in the last decade or so dynamic throttle behavior had been altered, first with IACV valves that stay open longer between shifts (notice the common rev-up on modern manual cars between aggressive shifts), and now artificially with e-throttles.