In the cases of Wade Flemmons and Betty Moorer I totally understand it, especially since the falsetto lead on Impalas "Speed Up" seems to get on most peoples nerves. Darrell has always been cheaper and easier than Doni, hasn't it? Apart from the fact that it's rarer, it's strange that Doni goes for so much considering that Darrell's has got a far superior vocal (IMO ofcourse... ). Very strange with the Shane Martin though, the Jimmy Webb version has got a punchier, moodier arrangement and better vocals, and it's still a £5 record. He's one of my all-time favourite song writers and most of his own recordings are superb as well.