AAM doesn’t matter much for most mech units, especially when you compare it to what Zerg can do with Vipers or Infestors. Tanks, Thors, Liberators (against ground), and Hellbats all hit for significantly large bursts, such that the bonus damage from AAM is usually far less than the damage from AOE spells such as Storm, PB, or Fungal.
Battlecruisers and Liberators against air are the two most heavily affected mech units, but Zerg can definitely still deal with them using Corruptors (or other anti-air) in conjunction with Infestors or Vipers.
Against the specific composition you mentioned, the Terran player’s army is usually slow and vulnerable to harassment, particularly when you get above a few bases. Brood Lords can still interrupt Ghosts or force friendly-fire from Siege Tanks (making their use a liability), and Blinding Clouds, Parasitic Bombs, or Neurals can easily swing a fight in Zerg’s favor even if you lose the casters in the process.
As for Auto-Turrets: Auto-Turret spam is a problem from a design perspective if nothing else. I am all in favor with its removal.
Abduct is definitely worth risking a Viper as long as you grab a good target.
Blinding Cloud (on Tanks/Thors) is also worth sacking a Viper based on how much damage it can prevent
Parasitic Bomb can also deal enough damage or force Vikings out of the air for long enough to pay off.
We are talking about Terran mech/sky here. Tanks (because of transformation time) and Thors are some of the slowest units in the game, and Liberators take almost as much time to setup as Siege Tanks. If Terran is forced to move their Liberators or their ground units because of Microbial Shroud, that fight is likely in your favor.
In contrast, Zerg ground units (with some exceptions) are some of the fastest in the game. Most Zerg ground units can take advantage of unsieged Liberators or Tanks trying to relocate.
Microbial Shroud can double the number of Liberator shots needed to kill units with more than 43 health, so unless your ground army is comprised of Zerglings and Banelngs (where the Liberator shots are usually wasteful anyway), then it will significantly improve you ground units’ performance when engaging the enemy.
Liberators target a 5-radius zone, about the same area as a Widow Mine. If your units can survive the trip through that circle, then they can effectively render the old Liberator zone useless and force a resiege.