I loved Nauvoo, but there is truly a special feeling the Sacred Grove. My great aunt who was semi inactive for most of her life, went on a trip in upstate New York. Her husband (who wasn't a member) stopped on the side of the road and told her where they were, and let her get out and walk around for the afternoon. (This was before they had a visitors' center or anything. I thought that was really sweet.
I think the Spirit there was awesome. I wrote some blogs about LDS sites to visit. So if you want to know more, you should visit them.
http://lds.families.com/blog/category/427&Start=5