As a TRAINING TOOL it's amazing. My 7 year old daughter had Anna and Elsa skating around in some pretty intricate patterns thanks to http://code.org/frozen.
It's not for heavy lifting, no.
In other words, "you're right, this saw makes a terrible hammer".
Event callbacks on a given room (for example) would make reacting to certain events much more efficient.
Say my code calls for a total of 20 creeps in a given room. I can try to create them all every tick until one returns a success, or I could create them all initially, and then only react when one expires for whatever reason.
Ditto for reacting to Enemy Incursions. I could either try to attack the nearest enemy with my guards every tick, even when there are no enemies to attack, or I could set some flag when an enemy appears and clear it when they're all gone.
You're letting people change the prototypes for their creeps, spawners, and so forth. Callbacks are entirely possible, they'd just need some code support and documentation.
If you can integrate something like Blockly, you'll vastly expand your audience.
It's a visual programming language that translates directly into JavaScript. It runs in the client's browser, though the blocks can be saved on the server. If were to disable the client-side javascript input entirely (only support code via blockly) you would eliminate a fair slice of the copy-n-paste issues. Folks would have to take screenshots, and manually "write" the scripts themselves...
Good luck.