*Not an official OFPEC statement on the issue*
Replayability is important because if a solid mission is designed to be a "one-shot wonder" never to be played again, then where is the value in creating it?
You spend 2 weeks hard out making a mission, the person completes it in 10 minutes ... and thats it? Throw it out from there?
Seems pointless, but thats just me.
In regard to your preference for a good mission, a good mission will always create a certain amount of replayability anyway.
Good mission = want to replay it, maybe a different way or even just the same way, etc
Bad mission = never want to play it again
Hope that helps some.
Anmac will be able to offer the official OFPEC word for you.