So I tried the no-wave-warning + cross-planet-wave combo.
Thing is the CPWaves are nothing more than no-wave + preemption. The AI sent its waves on its own planets and they are supposed to go for human planets via wormholes. On the paper, that sounds interesting. On the battlefield, waves become just preemption.
I could have added "preemption" to the title of this topic, but the problem, albeit the same, isn't a problem for preemption because it is what it is intended. Preemption is reinforcement redirected toward threat: no problem with that.
The problem with CPWaves is that waves are supposed to be attacks. If waves become threatening, there is no more attack, or only fatal ones. Then AI ships on player's planets occurs only if something goes wrong: threat massed beyond stoppable threshold or backstab when the main fleet moves. So players are going to avoid these situations and pay attention to cleaning threat (with preemption, this is OK, because it's intended), but there is no more AI ships at players' planets in normal situation, so no more salvage, and the reprisal/salvage mechanism cease to be a ping-pong game between AI and the players using scrap to send counter attacks at each other. Salvage is supposed to be player's reprisal mechanism, originally intended to give metal and !!fun!! and accelerate the rebuilt phase and make it less boring.
I see some ways to solve this problem.
Lowering the threat go-for-it threshold, in other words making threat attacking more early with less power, would be a way to make CPWaves stacks with each other and the normal threat and the optional preemption, and all of this attack without reaching 150% fatal attack. However, the threshold mustn't be too low because threat would suicide on turrets, ant this is not the goal. However, normal threatfleet would be much less threatening.
Then, this is the core idea (yep, I'm exposing lame ideas while I have the one I think clever in my sleeve).
CPWaves are release on AI planets but with a special "go-for-it" behavior and not a threatfleet behavior: they attack the targeted planet whatever is at stake, a bit like a regular wave slingshot through the wormhole directly on players' planet. Then, like with regular waves, nearby threatfleet ask itself "hey bob, these guys seem to have fun, will we join'em?" If the wave-d fleet make the balance change, threatfleet join in the attack, even if there is no doomsday crapload MkV fleet waiting for the players' fleet to move away and score a fatal touchdown in no time.
I feel I was a bit confused in my explanation. Maybe I should sum it up.
TL;DR:
Change CPWaves behavior from threat to go-fot-it to make them give scrap like regular waves.