Bukkit

1. Make elementals have different traits. Example -

Tree elemental
Treats villagers nicely
Kills all hostile mobs.
Kills anything that harms a villager
etc

2. Lightweight
The plugin needs to be more lightweight, less lag as if you spawn 2 elementals it could almost crash a 216 mb server.
Needs more lightweightness.

3. More added options in config
Enraged true/false
After 50% health gone it will attack faster and start to throw blocks at you.
Wave Smacking true/false
Will throw waves of rage against you, pushing you back and damaging.
4. More block creatures! Elementals could be much cooler also if there were different kinds! Mini elementals etc.

1. I'm working on the Ai now its very complex

1. Not much i can do about this the server needs update every block 4 times a second, per elemental about all that can be done is use less blocks.

1. The config files are very customizable and will expand them

1. You can make more! all the tools are there for players to make there own.