I don't think anyone has ever quantified what courage does. It is described as helping a planet's defense, but I think that this is a typo. If you check the debug, the game checks your courage status before beginning *ship to ship* combat.
Now, if luck helps with your attack rolls, then perhaps courage helps with your defense rolls. This makes sense to me. You have weapons/luck, why not defense/courage?
I have lately been adding courage as a matter of course, if for no other reason than curiosity, and my ships *seem* to be doing a bit better, and surviving just a bit more often than they used to. This is only speculation, though, and any difference that I am seeing could be nothing but my own wishful thinking.
Best advise- try it for yourself and see if you notice any difference in your land or space battles. It's only one point after all.
I would like to hear from any other players that use courage, and know their thoughts on the matter. Good luck.