Hi Mark-- provided you arrive on time, I think you will have ample time to jump into a car and come into town for a stroll around the city and have a nice lunch. It may be best for you to choose an area of town like Puerto Madero, so you can first walk around the Plaza de Mayo and surrounding areas and then have lunch.... or if you already know that area then maybe something around Palermo Soho...? Nice cafes, shops and plenty of places to eat. I assume you will be leaving all your bags at EZE or even have them checked through.... so the only thing I would do is once you sit down for lunch, have the place call in advance and book a radio taxi to have waiting for you at a given time, so once you are out of the restaurant you have a car waiting to take you back to EZE.

I assume you will already have your boarding passes for your next leg, so the only thing you may need to do is pay the airport tax and you can go straight to boarding... maybe its best to pay the departure airport tax in EZE before you head out to town, that way you can then go straight to the gates once you return after lunch.