I'm not sure about other sales, but if you look on Sedo for domains ending in "erz" (for example your camperz.com and hijackerz.com) you'll see that there are 266 listed and only 4 have gotten any bids. I think thats an accurate depiction of the popularity/value of domains ending in z.
I'd say list them on Sedo, if they don't get any offers by the time they expire, let em drop, IMO.
Who knows though, you might find an interested party.