What about Annual Super-Events? Seeing as its a convention city, there's naturally probably conventions of some kind going on all the time. But what if there's special collaborative events, rare events where the fandoms unite, if only briefly, to produce something truly awesome?
Perhaps once a year, there is the Cosi Gras, a Parade of the most spectacular cosplays from all genres and fandoms, with huge magnificient floats dedicated to all things glorious and nerdy, be it a 1:1 Paper mache Gundam or a miniature Normandy.
Or maybe the Festival of Suits, where everyone dresses in formal attire for a day. Like a Festival of Masks, where everyone hides their "true" self, but by dressing in immaculate business attire. Naturally all sorts of depraved sex goes on at night, whilst wearing this casual clothing.
The Infinity Christmas Santa Battle Royale is always a big hit with the tourists, as Santas are chosen to represent each fandom and compete to prove who has the finest Harbringer of Christmas Cheer.
A week later, the Infinite New Year is particularly troublesome, as the breweries throw open their gates, and everything from Romulan Ale and Mead to alcoholic dippin' dots are sold at low, low prices.
There'd be other, lower-key events on the Infinity City social calendar, of course. Valentine's Day being, in theory, a day when shy blossoming geek romances are given a chance to bloom, but in practice often produce many a cry of soulrending agony, when LadyVioletBosom turns out, all too predictably, to be your best mate Chez.