Hello,
I think it may be because you are using more than one Kind type. This would cause it to look for files with all of those Kinds (types) simultaneously. I don't believe there is an "or" function in the Smart Folder logic, which is causing the results to come up blank, since a file cannot be identified as Document, Image, PDF, and Text simultaneously.
You may be able to accomplish this with Automator, but I am not experienced enough with that to know for sure.
C