Yeah, you are right with the part about investors receiving a greater return.
As higher interest rates make it lucrative to invest in Australia, it will lead foreigners wanting to exhchange MORE of their own currency for $AUD so to invest here. An increase in demand for $AUD (illustrated by the shift from D1D1 to D2D2 will hence lead to the appreciation of $AUD (illustrated by the increase from P1 to P2). Like this:
[Image from Wikipedia]
Not entirely sure about the second part of your question, but I am pretty sure higher interest rates will attract more investors to invest, as I mentioned above. You're probably thinking of inflationary effects which makes the economy less favourable to invest in.