I did a couple half hour sessions and discovered that I make (on average) 650 graalats per 30 minutes at showdown. I won every showdown except for a few of them. If it takes you 20 seconds per ship, then ship repair gives you 990 Graalats every 30 mins.
Seems like even if you always win, showdown will not earn money as fast as repairing ships nonstop. Kind of lame considering how much more work it takes to win showdown vs repair ships. Ship repair is in a whole other league than showdown, recycling, and mining when it comes to earning graalats.