I'm fighting the invaders as well. Thus far no advanced tech components, they can still be gained from ruins though. As for them all being the PD craft, that seems like bad luck on your part. I'm getting a good mix of craft from them. Invader missile designs likewise are very poor for their intended roles, but they do seem to be mixing it up, it looks like the ai is trying to pick out how it should build its missiles.
I did however see invaders spawn in what I think was the location of a closed wormhole, they just appeared 200M km away from the existing wormhole and caught some stuff of mine by surprise. I think the rules are that they treat wormholes like jump points, and can only go as far as their jump drive distance rating can take them.