Read
http://www.sammyboy.com/showpost.php?p=149813&postcount=26
I was advising someone who has SGD500k sitting in the bank.
Exchange rates are not a factor if one is looking at yields over the long term. It has worked for me over the past 20 years.
Exchange rates fluctuate all the time but they affect only conversions not yields. Funds that aren't needed as working capital can therefore safely be parked in a high yielding currency. The Japs have been doing it for ages.
There will always be periods where exchange rates are favourable for
a) Buying more OZ/NZ dollars with SGD (as is the case now)
b) Converting OZ/NZ dollars back to SGD (some time in the future).
I have made money both from yields and from exchange rate movements.