Sexyv40,
Your journey to date is not unusual, having a desire to improve your financial position, having dabbled in property and made some money on some of your investments but having sold some decent properties to buy an expensive PPOR.
As others have said, you need to have a plan, a time table and a strategy to achieve specific goals. Not sure your journey has been that planned.
Buying in Kensington in 2010 may have been top of market so it is not unexpected there may not have been much growth since then. We have not yet been through a full cycle since 2010. Your purchase in Nth Melbourne, you probably paid the renovators profit. Melbourne is and has been a traditional low rent yield market, so you need to match your strategy to your current financial position in terms of location decisions.
To be able to retire, you need equity and income, so your goals need to incorporate how you can achieve both in your time frame and with your financial position. You need to be able to extract growth to help fund the next IP and also show sufficient income to enable you to obtain finance for the next IP. Growth may come from smart buying location, good price purchased, manufactured or simply a slice of luck in timing of the overall market, but I would not rely on the last.
The success stories are nearly all based on having a plan, a vision, a desire to achieve, a strategy and then action as others have said above.
Get the finance component worked out first, the property decision then follows. Good luck with it.