I wonder:
If Subaru has this common problem, there MUST be an aftermarket security solution for it. If not, I should quit my job, make one, and profit.

Might Subaru even make a bolt-on security upgrade if this is so common?

I also wonder how the thieves know to target you? Regardless, they know now. So, if you strip it to stock for a few months, maybe they'll hit again, find nothing, and be gone for good. Maybe a very stealth install is needed when you put the gear back in.

Last option: sniper rifle + rooftop = no more radio thieft.