A couple of other suggestions:

1)You'd have time to drive to Saratoga (The Northway entrance is very close to the Airport). Depending on where you are coming from, it may be very scenic. The City of Saratoga has a number of nice restaurants. It's off season (The race track is the main attraction in summer). It will probably be much more scenic than downtown Albany on a Sunday morning (Which will be deserted).

2)If you like shopping, Cohoes Fashions http://cohoesfashions.com/ may be of interest. I have not been there in a long time, and the quality of bargains may have been reduced, but it is a local store that you wouldn't find elsewhere. It should be open early on Sundays if you're traveling before the holidays.

Are you doing the mileage run on United? (Your flights sound like a round trip from IAD). There are frequent delays on this route (At least I get a lot of them)

Car rentals are convenient. Most have cars in the attached parking garage, so you won't need to use a shuttle. Arriving an hour before your flight is more than enough.

It has been unseasonably warm in Albany so far this season; that could change quickly. Be prepared for cold and snow.

Good luck on the trip!