Just got off the phone with Apple, to ask my first-world question...how much would I get back in trade-in on my (month-old) Series 5 if I wanted to get the Series 6 JUST FOR THE BLUE COLOR. Well...way short of enough, lol.
As for needing the cellular, I had originally purchased the cellular, but a week later traded it back in for the GPS only; the killer app for me did not work independently of my phone anyway, so that particular use would not benefit. And then I thought "when am I ever without my phone REALLY?" and decided it wasn't worth the $100.