Hey Gailforce,
Firstly, you may save a few bucks overseas, maybe even a few hundred, but remember, if it has a value of more than $1000AUD you will need to pay duty on it when you come through customs so dont forget to factor that in and the excess baggage you are likely to pay coming back from the US. Most US airlines are criminal with their excess baggage fees.

Kiteboarding is a small and competitive industry with most shops selling similar products at similar prices so what that means is it comes down to service and the relationship between the shops and yourself.
If you buy your gear overseas and come back to Oz and have a problem with it that needs warranty, I'm sure most reputable retailers will sort it out for you although I have heard of a few who aren't too kee and may make life difficult.

Don't expect them to fall over backwards for you when you denied them the chance of making a few dollars on the initial purchase. Your shop will support you and the community if you support them.
Example: Two riders return a bar for warranty, one customer bought his gear from the shop and the other, from overseas to save a couple hundred bucks. The retailer has only one bar in stock and the next shipment is due in 4 weeks. Guess which customer is going to get the bar???
It may pay dividends in the longer term to start to forge a relationship with your local retailer. They will always be willing to help their existing customers as we do with loan kites and boards, free tips and coaching at the beach, demos of new gear, advice on tuning and help with your gear new or old, free stuff from time to time and discounts. I think you will find that in time, this will far outweigh the benefits of a short term gain.
Just food for thought!
Good winds,