I've only been playing a couple weeks. I THINK I noticed when I upgraded my Chewy starting character to 4* after farming shards for him that the modifiers for leveling up a level increased? Is that right? If that's true would it not make sense to hold off on training your characters as much as you can until you've farmed shards to increase their star level?
If there is an advantage to be had here I think I'm in trouble. I've already leveled my starting toons to 40+