1) Top tier on AA, AS, DL, US. Mid tier on CO. Bottom tier on NW.
2) Complementary space-available upgrades (when the airline isn't trying to do everything possible to sell them for peanuts at the gate to avoid giving them away for free).
3) Yes. AA Plat for life.
4) Yes. Failed to match on DL, had to earn it; bad move on their part. Matched on AS, got me to requal the following year, so we both won.