Something like 50% of Brits who emigrate to Australia return within the first few years and in a rugby context, John Bateman has chosen to return quite soon so certainly the grass isn't always greener.
It is something that seems to happen more with the modern player though; many of our overseas signings of the 80s and 90s were here for 5 years or more. I don't think the weather was any more tropical back then, or Bridge Foot resembled Sydney Harbour more closely but I might be wrong.