alasta: For me the two main barriers would be my friends in New Zealand, and the logistical challenges of physically relocating. Relocating to another country isn't straightforward - you'll potentially need to arrange transport of your personal items, sell your car here and buy another one over there, open foreign bank accounts, set up insurance, find somewhere to stay temporarily when you get there, find somewhere to eventually live permanently, connect your phone to a local provider, learn all the local laws and regulations that might affect you, and on it goes. Oh, and having no credit history over there might prove to be an additional challenge.
Sell your car - yep, did that no worries, if you're single and living close to the city, you don't need to buy one here. Cars are more expensive here. Petrol is a little cheaper, but purchase price, insurance and rego is more expensive. But I spend an average of $5 a week on public transport, I just walk everywhere, catch the odd tram and once in a while get a taxi. Work's out far cheaper overall.
Open foreign bank accounts - really, it's not that hard. Apply before you leave, flick some money over here to set you up, visit the bank when you get here and you're done. No worse, and I'd say easier, than changing banks in NZ.
Insurance - again, it's not that hard. What is interesting is that most insurers don't offer contents insurance to just one person living in a shared house. However the RACV offer renters insurance, and it's about the same cost as I was paying in NZ.
Temporary accommodation - helps if you know someone, hostel living will get expensive long-term, but it's really not that big of a deal to pay $30/night (or an alternative, slightly cheaper weekly rate at some places) till you find somewhere permanent, provided you factor this into your planning/finances.
Connecting your phone - something you have to do if you're moving house anyway, which happens from time to time, it's not that big of a deal, plus if you're going into a shared flat, it's going to be set up anyway. Getting a mobile number set up is hardly difficult either.
Learn all the local laws and regulations that might affect you - really? sure, there are some quirks (they're big on fining people for jaywalking in Victoria, it's a bit wtf, but whatever), things will be a little bit different, sometimes unexpectedly. But to let that prevent you from moving somewhere is a bit silly tbh.
I had no problem getting a credit card with a bank that is not my everyday bank. They are big on the identification thing here - get a State driver's licence as soon as you can (you have to within 3 months in Vic to drive legally), it will be handy. You sometimes have to go to the Post Office to verify identity, or head to the chemist to have your statutory declaration sighted (e.g. for Medicare cover under the reciprocal agreement), but it's not that big of a deal. I sent some stuff to HSBC for id via AusPost, and I faxed them proof of my income and got a credit card.
In summary. It's not hard. It's no different to moving cities within NZ, and it's not much harder than moving house within the same city. You really have nothing to lose, especially if you're single (nothing's holding you back) and employable (there's plenty of jobs in most industries and they love kiwi's over here).
I was in a situation of having to move/find flatmates and looking for a job at the same time in NZ. It really made no difference whether I did it in Wellington or in Melbourne. I didn't have anything worth shipping, so sold everything, stored a few sentimental things at the parents and came to Melbourne with two suitcases. Three weeks after deciding to move. It's really no different than moving to another city, although it will cost you a bit more if you decide to bring the kitchen sink with you (not worth it for me though, Ikea + generally downsizing my crap made it cheaper to sell up and buy the few things I need here).
As for spiders and snakes, I'm not a fan, but I get by quite happily ignoring the fact they exist. Melbourne has a different climate, so snakes in the city is not really an issue. As for spiders, I've seen about 3. Smaller than any spider I saw in NZ. I had a bigger problem with spiders in Wellington.