Another example is as the game goes on once an Insane AV is had there's no more reason for Mercenary Discount.
I disagree. In fact, I would probably take an Insane MD before an Insane AV. MD is generally more useful than AV for getting to the first market, and Legendary AV is enough for every level that matters.
Keeping in line w/getting armies or saving armies. Thoughts on the next best Insane after Army Cache Boost (A$B) for getting armies?
If you're SAing quickly and so you're thinking about a second Insane after 20-30 SAs or so, you probably want A^B, as you spend an increasingly large amount of each SA on the early terrible levels. It reduces your desire to waste AP on IACP and also lets you fire off a CRA much earlier on every level.
If you're going JK_3 speed and taking another Insane every SA, then I'm not sure.
The only other artifact that directly gives you more armies is CB, and I don't think that's a strong candidate for Insane #2. Definitely for #3 though. I don't count A^B in this category because army camps are too slow to be relevant. Technically there's also TS, QS and AC, but actives suck.