It would help immensely if there was a gadget usage statistic implemented in MediaWiki.
Knowing the usage patterns of gadgets would allow to identify rarely used and too exotic gadgets that would be better used as a traditional user script. This would help in maintaining the gadget selection list at a user friendly size and would also help to prioritize gadget development.
In addition to the absolute numbers, the most meaningful information would be about "active users", with single-use testing-only accounts and dormant accounts excluded. A simple definition of "active user" could be someone who has registered more than two months ago and was active during the last month.
T27302: Enable UserOptionStats extension on Hungarian Wikipedia
T60196: Tool Labs: Provide anonymized view of the user_properties table
T61480: DBQ-197 User preferences usage on Portuguese Wikipedia