A year ago, they told Dad that the only way to fix these "sand blasts" is by replacing the windshield. He was having a tuff time driving into the sun, and sure enough that's what fixed his problem. He asked for a harder grade replacement glass. Hasn't had much issue since.
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac