Most of the increase in tourism probably comes from all the extra non-QF international direct flights to Melbourne. One of the reasons usually quoted by these airlines is the high fees and strict curfew in Sydney.
I'm all for more QF flights from all the big cities but QF has a dominate dom routes so can get anyone from Syd anywhere and have little incentive to do otherwise - at least until they start losing heaps of travellers to non-QF flights doing direct flights
Regarding the weather - we all forget we live on such a warm and dry continent, a significant number of travelers from other countries love our weather. Try staying in London, Helsinki or Toronto in winter, weather wise even our coldest place (CBR in my experience) would find this warm.
Let's face it we live in a great place - Syd has it's stunning habour, QLD warm weather and surf (plus rain forests), Mel has sports and arts, Adelaide has a beautiful city, WA a magnificent outback and great wineries, Tas has great forests. Our country is huge and diverse with significantly different cultures and even infrastructure.
Our differences and rivalry make it even better. I recently showed an overseas friend around Syd for 3 days and loved it despite being a strong Melbourne supporter/lover.
PS I must be enjoying being back after spending about 5 months overseas in the past 10 months.
