Hi Kiki,
I wanted to give you my view on this, as i have been battling with the same things as you. I have been here 6 years in Jan, and will be heading back to the UK in Feb. When I made my decision, I felt that everyone had an opinion that was beneficial to them, and they don't consider how you feel. What I have come to realise is that family are incredibly important, and are a lot more important than any location in the world. It is a hard place to make friends, it is not people are being rude it is just that our age (I am 32) most people are in different stages of their life's and aren't looking to increase their friendship group. Although I have some good friends here, I feel that the relationships I have made are lacking the same foundation that my relationships are based on at home. I think ultimately it is a hard place to live with no partner or friends. The main reason I want to go home is that if I am spending time on my own at weekends, and the evenings. I would rather do it, knowing that I can pop to families house as my family will always be ther. Other reasons for me are property prices, lower interest rate on mortgage, I have found I don't have to work as hard here (which I don't like), sacrificing holidays to go home for weddings, only 20 days leave etc, being so far away etc.
I think your concerns about going home are solid, but you don't have to go to the same job, same town etc. I like to reverse the way that I think about it, and think what will be the scenario if I don't make the change, and for me I can't see a future in Australia as there is nothing I really want here, or any reasons for not be close to home.
Personally I will leave with fond memories, but all good thing come to an end, and now I can't go soon enough!
Alex