Yes, always look on the bright side, Natalie.

So... given how Nami in canon says that her skills as a navigator as she built them pre-GL, does that mean Nat is going to have to re-spec Nami now that they're in the grandline?

If anything, reliance on the grand pose will equate her skills being wasted, which suggests this tabletop game is poorly written. Or as Roronoa "fallow the clouds" Zoro later shows us, neglecting a skill means being very bad at it no matter what tools you have for assistance.

In theory, it's still not wasted, just not shown that much.

Given how one piece weather/storms/etc are completely insane, I could easily see Nami's skills being used passively for the sake of convenience.

And we do know she learns to weaponize her knowledge later.

There's also how it would depend on the style of game being run. If a heavier focus was put on the actual process of the travel, instead of the time skips, we'd probably be seeing her using her skills every other second.

Any story of a fun battle with non-damage or/and non-lethal attacks?

I once tried to catch a rabbit.
My Shaprshift variant druid .. utterly outclassed by that furball...

Honestly, you should have known better. You never mess with wascawwy wabbits, they're only slightly less hazardous than canaries after all.

One of my favorite parts of Final Fantasy 12 was visiting the village of Playboy emblems; mainly because one of them sternly commanded that I keep my voice down and I wanted to say, "Be vewy quiet, we're hunting wabbits!"