Don't understand the suggestion for the Barclay Arrival Plus, that's not a card for people who travel in international J as it's just a fixed % back, where you can get a far better redemption by transferring to an airline program (again for international J, domestic coach is a different story).

The SPG and Amex Plat cover basically every international carrier except United. If you want United and want to put a lot of spend on a card, the United Club card gives 1.5 miles per dollar spent, that's probably the ticket.

If you want to earn Membership Rewards at a higher rate than the AMEX Plat, the Premier Rewards Gold is good as it gives a 15K annual bonus after spending 30K, plus 2x on gas and groceries, and 3x on airfare. The AMEX Everyday Preferred, while marketed to a different demographic, is quite good as it gives 1.5 MR per dollar spent as long as you make more than 30 transaction a month, and it gives 3X for gas and 4.5X for groceries (again assuming 30 trans a month).

For fun card to get the Ritz Carlton card from JP Morgan looks cool and gives you some Ritz specific perks.

The Chase Hyatt card isn't a bad idea if you like Hyatts.

And the Chase cards which earn Ultimate Rewards like the Sapphire Preferred are also quite flexible.

I think you've got your bases covered, if you want the combo of cards that allow transfers to almost every program you need one Membership Rewards card, the SPG card, and a Chase card (to cover United).

+1 for the suggestion on the Citi AA Exec, 100,000 bonus miles plus lounge access for $250 is a no-brainer.