I finally did it! I threw in the towel and am calling this painting done.
I've been working on this painting on and off for more than a year, and there's just a point where you have to stop, otherwise you run the risk of overworking it.
Although this is definitely on the bigger end of my paintings (3 feet by 5 feet), I don't think it was the size that was the hurdle for me. I actually enjoy working big because it allows me to work on one part, then while it's drying I can work on another area. It kind of keeps the painting alive. There were parts of it that went swimmingly, but then certain areas were just giving me trouble and I had to re-work them a lot. Part of the problem was that I was working from 2 different photographs I took on a trip to New Orleans, and although I knew they would be good spliced together, the point at which they meet was problematic. I think I worked through it, though.
Overall, I'm happy with the outcome. Being my harshest critic, I can definitely see room for improvement, but I'm also trying to take some sage advice I got recently and not try to make perfect paintings (it's never going to be perfect!).