Lowering saturation will make things worse. I've done plenty of tests with various settings when I had the E510 and I noticed that low contrast improves DR but not low saturation. In fact, it was the opposite. I have a pool with slide going into it. The slide is blue but because its old, the color has faded and it is now very light blue. When I reduced the saturation and took a picture of it, most areas were over exposed. But, when I increased the saturation to its max, then only a very small area of the slide was over exposed. The majority of the slide was light blue. So, by increasing the saturation, the camera was able to detect the light blue color of the slide rather than treating it as white. Thus, the DR was improved. This test proved to me that reducing the saturation does not improve DR, on the contrary. I used Natural with Sat +2 on my E510.
From what I've read, the E620 is a much better camera than the E5nn. It has a better DR and produces sharper images. So, it may be worth considering an upgrade. As I mentioned initially, the E510 is a nice camera and images are good right out of the camera. But, it is very aggravating as well because of its limited DR.