For me, there is nothing more aggravating, than trying to use a camera, which refuses to shoot. You, you can half press, recompose, and shoot. But a bad autofocus cam, is a PIA to work with.
When you push the shutter, and the fish swims on by, and then the camera takes the shot... Yikes!
If the strobe you get, for sure could be used with the housed gf1, then that should be ok.
But if it is specifically for the sealife, forget it! Don't invest more in that.
What strobe are you thinking about?
For me, the gf1 would make a world of difference to the joy and pleasure of shooting. Even if you might arguably get slightly better images with a strobe on the sealife, you won't have nearly as much fun.
You can shoot raw, and try a magic filter, or ur-pro, and vastly improve your IQ that way, as well as get much better video.