Perth and WA have hundreds if not thousands of (local government) parks, gardens and beaches. Most of these are well maintained and attractive places and suitable for wedding ceremonies. Generally you need to contact the Local Government city or shire council office to get permission to hold your wedding at these places. They are generally quite cheap as well.
There are many advantages to using such parks, gardens and beaches. They are public places and parking may not be a major issue. They are generally well maintained and pretty places, great for photo shoots. Many are quite scenic as they are in special locations eg beaches, war memorials with their rose gardens etc. You can be local to where you want the reception, or even have the reception there!!
The down sides to these local government parks, gardens and the beaches may be parking if you want it at a busy place eg Scarborough Beach at 2pm on a sunny summers day. It may not have special access facilities such as ramps or paths. It will quite often NOT have toilets close by though a few do.
if it is a public place you may have onlookers though in all over my 2000 weddings I have never been interrupted by onlookers. It may be windy as in Perth on a summers day the sea breeze can be quite a force to reckon with. Generally you will need to bring a wedding supply company to provide chairs, runner, table and may be even an arch. Often there is no power available for PA’s etc.
So go to parks you may be interested in and just have a look.