After reading countless forums about whether to drain (and fill) the ATF in my 2010 G, I decided to go for as the jerkiness of the trans started to get really noticeable and creaky on cold starts. The car has around 170km and never had a change before. After a couple hundred km, it feels remarkably better than before - way less jerkiness between gears (going into 3rd was always an issue), and cold starts are smoother. Just my experience.
Old ATF looking nice and dark.

 

I would drain refill it once more after 500 miles

 

Stick a magnet in the old fluid and see what you find

 

Yup I recently did mine as well. Pretty dirty.