All great insight provided so far. I would just also point out these features:
MQMs rollover so if you get to 60k, next year you start +10k.
Skymiles are terrible, but since there is no chart sometimes they will surprise you - just booked 4 in Y to SLC for 10k apiece. If you want Aeroplan miles, get them from credit cards.
DL Gold can almost always get Comfort+ (free drinks, snacks and more legroom).
Amex Business Platinum ftw (lower fee).
Biscoff cookies.