On that itinerary I'd probably make Huangshan my touch of nature, instead.
Is that just personal preference or are there other reasons to favor Huangshan? I had considered it previously. Its looking more and more like I will have 4 extra days. Also, I should point out that my arrival date is 4/30, so I know there is labor day on 5/1, which is why I was thinking it would be better to stay in the city on that day instead of rushing towards the water towns and national parks on a holiday. Not sure how crowded things will be on 5/2-5/3.