I don't think scripted enemies showing up every time you salvage would work.
First of all, it's kind of gamey and immersion breaking (I'm in the middle of nowhere and haven't seen a soul in days, and have flown around this system without seeing anything, but if I salvage something, a pirate fleet shows up without fail? Where did they come from?).
Also, there are implementation issues, for instance, should the pirates scale with your fleet so that the combat is relevant? If so, then you will have to have massive pirate armadas constantly showing up out of nowhere in late game. If no, then you just add another chore to salvaging.
Also, when you kill the fleet that shows up and salvage it, does that spawn another fleet?
I don't mind trying to make sure that salvage is accompanied by combat, but it should be done by having salvageable things in the proximity of existing enemies (which works fine with existing mechanics), rather than scripting enemy spawns every time you salvage. The game already kinda does this with those systems full of scavengers. I would like more of that.
Also, I don't mind explicit salvage traps, like where you salvage and then get a message that it was a trap and a pirate fleet is inbound, but that can easily be done with existing mechanics IMO. No need to make me sit for 5 seconds doing nothing every time I salvage something.