I know a little bit about JDAM's and in my experience these dummy concrete ones were used for practice on the range. Interesting, you learn something new every day. I imagine these are being dropped mostly by B-52s?
Probably not. A BUFF is overkill if you only need two to four bombs on a particular target. Heck an F-16 or F/A-18 can do that job. If you need a few more, send in an F-15E.