I stayed at the North DFW Marriott several times a few years ago.

FWIW, I would request a high room on the airport facing side and brought a radio shack type of scanner with me, with the aviation band (118-136mhz), and watch & listen to the activities on the 5 runways clearly in view below. The guys in the tower are simply amazing given the amount of traffic they are handling especially around "rush hours". One pilot even remarked at the incrediable job this one guy was doing, giving rapid fire instructions in a clear and concise cadence. You can get the frequencies for any airport at airnav.com if so inclined.

I was studying to be a pilot at the time and found it very helpful in earning my license. Also, there was a small park adjacent that was good for jogging laps around.

Once I went to an American Airlines muesum or visitors center that was definately on the south side. It was free and a decent way to spend an hour, a good IMAX movie of flying that was a bit of a commerical for AA. It was free but don't know if its still open. Perhaps the hotel shuttle bus will take you to and fro?