Is a spunked cock really about as useful as a spent match?

That depends. For a match that's been struck and the flame been applied, its effective life is over, whereas a cock that's shot its ball-load will, given a little time (variable), return to its former potency and potential.  It's only a shame that sometimes one has to wait quite long, and even then it only very rarely performs at the same level. I recall managing to cum four times all in one night with a guy about the same age as I then was, but that was exceptional and when I was much younger, full of vim and vigour, and that being the only time. In a multi-man orgy, the owner of a spent cock, unless he agrees to being the passive one, will often find himself reduced to being a mere spectator - and many of us find being the receiver of another guy's spunk, piss, spit or whatever when recently de-spunked yourself is nowhere near as pleasurable as when you've still got lead in your pencil.  Of course watching others pumping away is all very good though not the same thing, or carries the same satisfaction, as being actively involved.