OK. I rang a friend (old neighbor) to check out the roof on our old house in Sydney. Verdict is she said it is a little bit difficult to tell as the paint looks fine but the roof could use a good pressure clean as it is pretty mouldy. The roof was painted in 1996, so around 18 years ago. I do remember the new owners asking when we had the roof done as they though it had been done prior to selling not 12 years previously.
We did it again to our house up here in Cairns just under two years ago. This is a pic of the terracotta colour, the tiles were really porous, absorbed moisture and were really mouldy.
This is the colour after pressure cleaning
After paint
We ended up painting the gutters and fascias a very dark grey/black as they used to be cream. Painted the roller door Grey, it used to be cream. We also did the driveway as it used to be terracotta with a black fleck through it now its grey with a black fleck through it. I reckon it took 10 years off the look of our house. I have no regrets and I reckon it has been a good investment.