I actually think we should have made “all clears” worth something like 50 or −50 karma (if you get it right or wrong), and “NUKES INCOMING!” worth 300 or −300, partly for the reasons you mention, partly because you’d generally expect LWers to avoid nuking most of the time, partly because doesn’t really feel worth 1000 karma to correctly guess “all clear” 5 times, but does feel worth a few hundred karma to correctly guess the one incoming nuke.
I actually think we should have made “all clears” worth something like 50 or −50 karma (if you get it right or wrong), and “NUKES INCOMING!” worth 300 or −300, partly for the reasons you mention, partly because you’d generally expect LWers to avoid nuking most of the time, partly because doesn’t really feel worth 1000 karma to correctly guess “all clear” 5 times, but does feel worth a few hundred karma to correctly guess the one incoming nuke.