You don't say which neighborhood in Folsom you are asking about. Usually here in Folsom, if a home backs to any kind of open space then it is considered a premium lot and a buyer will pay more than one that backs to a home. Here in Folsom we don't have a lot of yearly creeks, so I am wondering if you are seeing a "seasonal" creek (water in it during rainy season) or perhaps a "wetland" that is more like a very shallow pond during the rainy season.
When purchasing a home, the seller will be required to give you a "Natural Hazards" report. In that report it should tell you the property is in any kind of flood zone.
Snakes and bugs are a common to all of Folsom. I can't say that you will have more than any other area. Even if you do, you will also have a lot more birds to see and listen to.
All thing being equal, same house, one backing to creek, one that does not, more buyers would pick the one backing to the creek. It would have better resale value.