I had good luck with my priority luggage as well in the past. I haven't had to check any in over a year now though.

Upgrades on EWR-SEA are rough. I've flown that leg as a silver and gold for 4 years now and been upgraded a grand total of 4 times. 3 of them were in the last month, but I was traveling on: Thanksgiving Day, X-mas Day, New Years Eve. So even though I was only silver at the time, I made sure to stack the odds in my favor. Otherwise my ratio for "real" flying was attrocious.

I had better luck with my various SEA-IAH legs, probably getting around 50% as a Gold, and maybe 25% as a Silver. (Far fewer legs as a sample though, I am EWR-heavy.)

As a SEA-based traveler though, I can't recommend the President's Club enough. The SEA Club is fantastic, the ladies who work there are professional and friendly, they recognize all their regulars...they just love their jobs it seems. I use the PClub even when I am flying AS/NW/DL from far away gates, if time allows.