I've noticed now a quite significant drop in mob spawns over time. The first time it happened I reset with a /cofh killall but I've noticed a drop off again. I'm pretty sure now it's a result of of the dungeons and creepers. The creepers explode the blocks and the mobs pick those blocks up and don't despawn. Often they end up trapped in packs at the end of water streams and eventually they exceed the mob cap.
I'm also concerned that I am missing something. I've been playing in my LP world for quite a while now and I have yet to have an invasion. Is there a config option that I am missing or was there a change at some point.
I was wondering why my night times near my base seem to be safer lately.
I haven't seen one either.
I did experiment in a creative world and the digger invader will give up when mining obsidian or 4x compressed cobble or higher. So, if you can catch one, they make pretty impressive chunk loaders.