I've actually been doing pretty much nothing but fallen spire campaigns at 8/8 ais lately. I suppose its not even the whole '1 aip is precious' as much as 'this collection of metal wont even build a single ship'...
As Fallen Spire is the only thing I play, I can agree with this. When you're building ships with costs in the millions, each, you tend to not notice a rather paltry 600k. So far, of what has been suggested here, the best ideas I've read were Draco's scrap one, or that nodes fill a % of your max metal, rather than a flat amount. Given that 600k was 60% of the previous max metal storage, that % seems fair. Now, of the two ideas, the scrap one sounds best to me. Gives me a reason to keep them alive, or, if they are on a world that is going to be painful to take and/or I'm low on metal, I can raid for some quick cash.
Why not combine the 2 ideas? While alive it boots scrap gain, (Human & AI) when killed it give you metal equal to 30%-60% of your current max storage. This returns a bit of randomness to them. Or, go with a flat %, with no randomness, but when popped it gives the AI 1 level worth of reprisal. IE, if you currently didn't have any reprisal wave warning, it would go to 1. If you had a warning of 10, it would become 11. This gives a drawback to popping them, but doesn't cause an immediate response.
