After playing with it for a while, I really like the variety this adds to the missions. If I had anything to comment on, I'd say that maybe the station defense missions are a little too easy to make money with since you can usually expect the station to do most of the heavy lifting anyway. They end up being way more profitable than running around doing bounties and exploration or commodity trading, and you don't even have to go anywhere in comparison. Maybe cutting down their cash rewards somewhat or making the reward something like a (20-40% baseline minimum scaled off the current rewards + an extra bonus for how much damage the player's fleet did) could make it feel more balanced?
If the attackers could also be real diplomacy factions rather than just generic "pirates" to make the player's rep with them fall by a few points as a result of taking such a mission could also add another layer of depth and decisionmaking: Maybe the pay for doing a station defense mission seems really tempting, but I realize it's a faction I really don't want to lose rep points with right now or one that could tip over into that -50 Hostile range. These sorts of mini decisions come up in the gameplay loop all the time with routing bounty hunting, exploration, or smuggling runs, for example. If all you're after is money, there isn't usually a reason not to take a station defense mission unless you have some other time-sensitive missions running.