Hi,
As part of their IEG [1], Eran and Ravid have mapped the gadget use in all
wm projects
https://meta.wikimedia.org/wiki/Gadgets
It gives a good overview of gadget popularity and may help to discover
hidden gems.
Cheers,
Micru
[1]
http://blog.wikimedia.org/2014/04/22/visualeditor-gadgets/