Wild mushrooms can be good for you. It's always best to know what you are doing before you cut them off willy nilly. There are only four species that I can safely identity and eat in the wild and they are:
There are other edible species, but those are the only four that I trust myself to identify through books and through friends who are well versed in mushrooms. I wouldn't start eating wild mushrooms based on my blog, but I would encourage you to read up on them and when you feel 110% comfortable being able to identify them, then try them.
As for the tree issue, from a wildlife perspective, so many birds and animals need dead trees to survive, that I support them being left up when possible. One of the reasons we are losing red-headed woodpeckers is because of the lack of dead trees with soft enough wood for them to nest in.
Here is an informative article about sulphur shelf on trees by Rosanne Healy, Department of Plant Pathology at Iowa State University that came out on June 27, 2007. Even she says, "If it is on an acreage, and not likely to do irreparable damage should it fall, it may be worth considering leaving it alone."
That is the situation with the oak that we found with the sulphur shelf.