Sorry this isnt an issue, but I have no clue how to suggest something.
I feel that you should add an option that allows signs to activate spawns and deactivate them. It creates precise control of spawns. There are some ideas off of Tribu that you might like.
Anywho, a spawn sign would be like TribuSpawn Spawn2 ON, TribuSpawn Spawn2 OFF. When hit with redstone, it toggles the spawns. Heck, you dont even need an OFF sign.

Another suggestion is Zombie targets. When spawned, the zombie will latch on to the closest player. By latch i mean, hunt, and never lose sight of them.

Im sorry this is in the wrong spot, but if you look into Tribu, you could have one of the best zombie plugins out there.

I have made a stage based off this design, and it has worked marvelously. You can watch the Kino Der Toten flythrough video if you want to take my advice.

http://www.youtube.com/watch?v=Hz0wq-qvjHA

For your first suggestion:
The next version uses power, which allows redstone to turn on spawners and open passages. This means your suggestion is already working its way into Ablockalypse.

For the zombie targets (2nd suggestion):
Targetting is actually very complicated in Ablockalypse. To explain this in as simple a way as possible, Ablockalypse uses a replacement for the Minecraft pathfinder, a type of pathfinding method called A* Pathfinding to move mobs. The way this works in Ablockalypse is as follows:

1. The mob spawns and is assigned a barrier target.
2. The mob breaks the barrier (or walks through it if broken), then finds a player target.
3. The mob constantly moves towards the player, at a slightly faster speed than normal.
4. When the mob gets within normal Minecraft pathfinding range, it uses the normal pathfinder (it looks smoother).
   NOTE: If a player dies after being targetted or the mob stands still for more than 5 seconds, the mob retargets.

I will not be working the plugin in with anything, although add-ons can be made for Ablockalypse to allow integration. Thanks for your suggestion!