I've had some success with AutoIt, but I'm not too keen on the BASIC language that it uses. It does the job, but has some quirks such as not really supporting empty arrays or lists, and it's not terribly fast. Also, the discussion boards are extremely hostile to any discussion of game scripting, even scripting of offline solo games like Minesweeper.

Would my existing AutoIt scripts for automating Plants vs Zombies be welcome here as examples of what I will be trying to achieve with MacroMonkey?

Yea, the main reason I didn't like AutoIt was because of it's syntax (although LavishSoft script for example is IMHO much worse).
Although I suppose in the end it's more preference of a particular style(s).
And I'm sure AutoIt has advanced a lot since 2005 when I started making MM.

MM is more compact and probably faster. Don't have published timings of AutoIt to compare too though.
Since MM uses LuaJit is typically faster then most script languages like Python, Java, etc.
And once LuaJit 2 is out of beta I port over to that. This new version timings show it to be almost as fast as gcc C!
Anyhow speed is not everything and there are several Lua vrs Python, etc., articles; not trying to start a war here.
Important design goals of MM was to be compact and fast, and not to be dependent on .NET (need not even be installed), etc.

MM uses a more modeler/encapsulated, more object oriented approach then AutoIt.
I.E: MacroMonkey's "gui.Window()" (using a table namespace) vs AutoIt's "GUICreate()" (embedded/prefix namespace) style.

Although AutoIt has a big following so there might be more help on their forums.
But like you say, they apparently forbid any game hacking/exploiting/bot related discussions.
And IMHO people are quick to jump in and flame there.

Feel free to post your game scripts here as there might be others that are interested and more to contribute et al.
Maybe a good spot is here viewforum.php?f=15&start=0
It's probably not that difficult to port one over to the other.
I studded most exiting script system when I started and continue to study and add more features.