Hey MudWasp,
I was also wondering what constitutes a successful bombing mission. I consider it successful if I or someone from my flight hits a target. If no one from my flight hits it it's a fail (even if the other flight hits it). I also add 1 point if I personally hit a ground target.
so just like you had it:
1 point if I hit the target
1 point for successful mission (target must be hit by anyone from my flight)
1 point for landing at home airfield.

That is until I was flying bombing missions. Hopefully I'll get to fly a plane again that carries bombs.
I was never able to get a 4 point mission: bomb a target and shoot down a plane.

"Take the cylinder out of my kidneys,
The connecting rod out of my brain, my brain,
From out of my arse take the camshaft,
And assemble the engine again."