Melanie, do you know if the new flights will be later or earlier than their current flight? The current flight leaves around 4:45 or 5:45 pm depending on daylight savings time and it is great because it gets you into Madrid at 7 in the morning. I just flew on that Iberia flight from Chicago, and it was pretty comfortable. Everyone was very friendly and helpful (I never understand all the complaints Iberia gets about rude flight attendants), but the food was probably the worst airplane food I have ever had. I don't know if the crisis means they're scaling back even more on food, but it was really a new low. And I am not a picky eater.
If you book your ticket through American, as a codeshare, you can't get a seat assignment till day of departure, which is a pain in the neck. But I always stick with AA because they are much more helpful and efficient if you need rebooking.
The real plus of that Iberia flight is the early arrival. Immigration is usually empty and you just sail right through, and our bags were on the carousel by the time we got there. Later in the day things get bogged down a bit, in my experience.
My T4 tip -- always take the elevator, some of those escalators go up three or four flights.