You're kidding yourself. As soon as you move into your PPOR you're going to be emotionally attached to it. Extra money will more likely be spent renovating the thing or buying things to put in it.
And every dollar you DON'T pay into the mortgage, but buy another property instead earns you more than 7% a year over the long run. By trying to pay off your mortgage you're decreasing your leverage, and the opportunity cost is all the assets you DON'T buy because you're chasing a 8% return on your money. It's no different from saying 'I'll put my savings into a high interest bank account instead of buying investments'.
At first, anyway. I can find metropolitan properties yielding 5%. With the 7-10% increases we're seeing in rent.... in any case, it wasn't so long ago that you COULD get neutrally and even positively geared properties in the capital cities. Those times will come again if prices go down, rents go up and interest rates go down.
Your logic is fine, but you're not seeing the bigger and long term picture. Your plan is to aim to not lose: you're focusing on not taking risk. As a young person with a good income and no dependents, you can afford to take more risk.
Alex