Being the type of person who likes writing useless scripts that no-one uses, I decided to gather some metrics on larger (>1000 lines of code) MyBB plugins.
I've pretty much randomly picked these, and the list is by no means exhaustive. So feel free to suggest more (should be larger ones) to add to the list (though it must be easily retrievable by me - ie I don't need to jump through hoops to obtain it; you can PM me ones which are like that and you can remain anonymous and I won't share/use the code).
http://mybbhacks.zingaburga.com/plugin-metrics.php
If anyone's interested/has doubts, here's the script I'm using to collect the data.
run.php (Size: 3.32 KB / Downloads: 437)
A list of limitations of these stats can be found on the above page.