I love it too, there's a lot of beautiful (albeit ruined) architecture to see for such a small city and it doesn't take too long to walk its entirety. I hiked Pacaya as well, not surprised about your dad's shoes... that heat gets intense. Would have loved to do a trip up Agua as well but I lacked the time. There aren't many other places where you can get so up close and personal with so many different volcanoes.
It's a wonderful city. I was there for a wedding and we had a blast. One thing I really appreciated was that the wedding there didn't have people eat a big plate of food and then cake and then expect people to dance. They expected people to dance immediately and food was out the entire time and you could eat at your leisure. What a great time. It's a city I'd like to return to.There aren't many other places where you can get so up close and personal with so many different volcanoes.
I really was shocked by how close you can get to the lava flows, literally jumping over them. In the US you would never get that close. -Really, you probably shouldn't be that close.