I commuted for several years MCI-DCA weekly and always used US Airways. The operation at MCI is small...the people there seem to know their regulars and are a pleasant bunch to work with. (At least it was a few years ago...)

Although you may not love UA, having access to them in a pinch is handy from MCI because they get you nonstop into all of the various *A hubs. When it's Australia time, your trip will likely begin with MCI-SFO on UA.

You also have MCI-IAD as a backup on UA if you can't get your normal MCI-DCA flight.

Have you selected your housing yet for the DC work? I didn't stay in hotels there either: we had a contract with Execustay by Marriott. If you have a choice, take a look at them - when I was there they had tons of units both in DC and right outside DC in VA and MD. I ended up in a place right in Rosslyn - far, far better than dealing with hotels, even with all of the points and the status that come with hotels. (I was given smallish lump sums of MR points every quarter plus Gold status. This was before Execustay was formally/globally included in Marriott Rewards.)

SPG Amex is an excellent credit card in general. Even relatively small amounts of Starwood points become valuable as "Cash & Points" rewards. With either the Marriott or HHonors programs, it's a long, long haul to reach the high award levels where meaningful value is achieved. And that's hard to do off of the CC alone...