Thank you all. UA's pricing was all over the place today, and I found nonstops in both direction, regular economy class, for about $300 more than the flight with the FRA layover. I took it and cancelled the other. This is a good result, although it does mean that now I get to spend the next 24 hours obsessing over this. The Delta flights were one stop both ways about about the same price as this, so I consider this a good deal.