I really like the idea of this mission. The game overall needs more variety in the tasks you can do, and this mod is a great first step in expanding it.
I think I'm going to restrain myself from doing more of these missions as of yet, however, as I've found that it's far too easy to successfully complete the mission and be paid in full without being able to even see the invading fleet, as the System's defenses can sometimes easily deal with them without even reaching the station. I'd recommend that Mission rewards to be at least partly scaled to depend on your contribution to the destruction of ships of the enemy fleet, similar to System Bounty contracts. The factions are just giving Spacers taking these missions free money otherwise.