Places I used to take my 4.2 center console.

River -  Flathead, Bream and Crabs. Mully's at night if your very keen.

Cockburn Sound - Squid, Pinkies (In Season) and Gummy's (Still nights) Plus the usual Herring, Whiting ect.

Behind GI - Skippy, KG's and Crays

5 Fathom Bank (Weather permitting) - Pinkies, Dues (occasionally) KG's, Skippy

Logue Brook - Trout

And and Electric motor and you can add Harvey into that too - Trout and Redfin

If you are ever inclined Moore River is an option, fairly consistent for black bream, easy on bait but harder on lures. I have camped up there a couple of times which was really enjoyable and have caught quite a few prawns at night around the mouth.

 I think your in a good posistion to kick some fish butt if you have a decent 4wd .....

 Its a perfect size and wieght craft to set up as a specialized beach fisher , with a h/d trailer , bigger tyres and drawbar extension.

 Locally as mentioned you got the sound , the swan , point perron area , covs reef , crabbing at mandurah etc etc 

 but if your setup well you have beach launching and great fishing at lano , cervanties , horrocks , and sharky bay ( perron) to the north 

 and places like peaceful bay , walpole , ocean beach ( denmark ) bremer etc etc ,,, almost anywhere theres a firmish beach 

 and a way out thru reefs etc , you can really access some less fished waters that all the big boys cant reach...

 I mean even Rotto from Woodies or Freo on a really nice day ain't off limits. 

 I'd begin with the bays and rivers you've mentioned, plus trailering to similar spots up and down the coast, like Ningaloo lagoon and Nornalup Inlet. Given you've had previous experience I would also think some inshore areas would be no problem if you pick your days and plan for possibleweather changes that might make it an uncomfortable, wet and slow trip back. Allow some extra fuel accordingly. Most of my fishing is nearly all  inshore of or out to the 3 mile and  have had many great days, but I watch the weather forecasts closely ( use all three to help decide - Fishranger, Meteye & Seabreeze), trying to find days with swell <1.5m and wind <12 knots

 my poly 4.1 has been out to the 40 and 50m marks metro- pick the day and be prepared to cut it short if weather changes

been to the muirons of exxie  warroora and ningaloo station- fishing outside the reef

much more stable than a tinnie

at ningalooo i often drift over the reef  tilt motor up fully - who cares if the boat hits reef- it doesnt do any damage

 Awesome thanks for your responses. Much appreciated. 

I do have a fourby set up for off-road, so beach launching is definitely an option,once I put some better wheels on the trailer. Going to spend some time in the river on her getting used to her and making sure she's good and reliable before venturing too far afield. She's not quite idling right at the moment so a bit of carb cleaning/idle fiddling required. 
 

thanks again!

 The locals will take a 4.1 and smaller from TI to PNG without batting an eyelid. As long as you've got good weather, plenty of fuel, a sense of humour and all the right safety gear anything is possible in a 4.1m boat.