I've started a new game+ and after about eight hours I am close to the end of chapter 7. I did a level reset to 1 for all of my characters, but I skipped almost all sidequest up till now. The game is a lot shorter the second time around. Of course it all depends on what you plan to do during new game+.
In the first Xenoblade Chronicles' new game+, I completed playthroughs in 10-12 hours while defeating ~150 unique monsters to pile up affinity coins.
Dang that's fast! I'll probably revisit the game later on then, perhaps even force myself to use Rex and Morag... maybe.