Since find does output directories, and clearly you don't want to grep on them, why not just do something like

find . ! -type d | xargs grep

To be even safer and work with any file name (containing even newlines), you actually need to do

find . ! -type d -print0 | xargs -0 grep

So maybe you just want to alias this whole thing :-)

I don't think this a reason to keep GREP_OPTIONS, but like I said I don't mind if it is kept if at least people are warned about how it might break shell scripts.