Have a look at the ERSA AD section on approach lighting- there are from memory 2 different types in use in Australia.
When getting visual, a quick count of the lights will give you a distance (or know beforehand how many you will need to see), and also don't forget the 500/1000/1500ft markers etc.
Cessna, some aircraft may not have the ability to measure the ILS dist. on the chart... And like you said, on slope...
But if you can get that measurement then that makes it somewhat easier to judge the visibility!