Hoi,
I am not to judge what conferences will be deemed relevant for an item in Wikidata. When a conference is relevant, it is the talks and particularly the registrations of the talks, the papers and the presentations that make the conference relevant after the fact.
Is Wikimania relevant? Absolutely. Do the Wikimanias have their own items; they do and nothing changed there.Is it relevant because of it being a Wikimedia "thing"? That it is as well and as I have said on a different mailing list as a community we are exceedingly bad in recognising what we do and have done.