Just got back from the local spring shop. I went to buy center bolts and leaf clips, but while there I asked about both new springs, and re-arching old springs. What a surprise!
The guy said re-arching old springs isn't worth it. Not because it won't work, but because of the cost. His shop starts with a flat fee of $55 to take the spring apart. After that, the labor is charged at $77/hour. He said typically it runs about $175 to re-arch a leaf spring, and they sell them new for $130. He told me one guy had a foreign car that they couldn't get new ones for, and it cost him $300 PER SPRING to have the re-arched.
He also showed me their book, which says that there could be any of 12 different OEM springs in a Cherokee. They carry six -- two are lower spring rate, four are heavy duty, all with the same 745 pound total capacity but with different initial arch dimensions. Unfortunately, his book does not list the spring rate by pounds-per-inch, only the total capacity.