This is definitely a case where, "Whatever you believe is right, is right".
For me, sometimes I care enough to upgrade and sometimes I don't. On free trips to Europe, sometimes 1st is very nice and sometimes the top deck is a lot more fun (especially coming home). I am specifically flying coach on an upcoming cross country trip just because I want to try the new UAL Premier Zone.
I spend enough time crammed into tiny little commuter planes to know for sure that coach won't kill me, but by the Grace of God and Good Planning, I can make my decisions based on my mood without a lot of impact on my Mileage Account balance.