Are you talking about a personal import or a SEVS import? There's two different ways you can import an R34 or V35 for example.
Personal imports have to have been owned by the importer in another country continuously for a year, with evidence to prove this (purchase docs, service books, insurance invoice etc). You must also be coming back to australia with the intention of settling down, not just visiting, and again, you need to supply evidence of this. You still have to pay taxes and for compliance, however the taxes aren't as high, and the compliance is a lot more lenient.
SEVS cars have to have import approvals given prior to the car even getting on a ship, the import approval is issued in australia. If a car was to arrive in the country without an import approval then its either re-exported or destroyed. Import approvals can only be applied for SEVS cars by RAWS workshops on behalf of the customer.
Its one thing buying and loading a car onto a ship, the uphill battle is when the car lands in Australia with the paperwork and the regulations.
Its also here that the costs of an import blows out. You have to pay taxes and duty on the car, then you have to have the car complianced, meet roadworthy standards and finally registered for road use. All that can add anywhere between $5000 and $10000 to the FOB price + shipping costs (depending on the cost of the car, and the compliancer). Then you have the dealership put their profit margins on it.
To answer your second question, most insurance companies here can cover V35's, and if they don't, they usually have a sibling company that handles collectible, rare and sports cars.
A user by the nick "Rezz" on the forum I believe brought back his R32 as a personal import when he moved back from Japan. You might want to ask him how he went about it and his experiences.