As far as I am aware, the term "Brisvegas" originated as an ironic association with Las Vegas, to pay out on Brissy's less-than-perfect nightlife scene and perhaps its general "things to do" factor (at the time). And yet, while meant to be an insult initially, recently Brisbanites have "reclaimed" the word, of sorts, as an endearing term for a city that, while not exactly being "where it's at" in any sense of the word, is still a pretty cool place to live.
To take the mickey they started to nickname their town 'BrisVegas' because it was nothing like the 24 hour American party city.
The nickname stuck, and as Brisbane emerged as a modern city sometimes the origins of this nickname as mistaken and taken to mean that Brisbane was likened to Las Vegas - when it was the opposite.
According to The Age: 'A staffer from Brisbane's Time Off magazine reckons it was coined as a result of an Elvis tribute CD it put out in 1994.'As do I. The term never existed before this, but within a few years was adopted idiotically by Brisbane yuppies, who had no idea of said indie CD compilation that coined the term. Another example of indie culture seeping into the mainstream, and its origins being forgotten.
Connection to Las Vegas... It seems to have been coined when they decided to turn a lovely, but derelect building in the heart of the city into a casino.