Everything helps, so I think it is worth considering the starter stopper.
Depending on where you are parking your car, and if you have keyless entry and button-start, also consider shielding the keys when it is parked at home (especially if parked in an open driveway). One of the method of steeling the cars is a relatively simple method of amplifying the key signal so the car will open and start. There are also shielding pouches for keys for when it is parked away from home.
For those with automatics, there is a nifty pedal locking plate for the VF available on eBay. It’s probably not something you’d want to use every time, but it definitely would be worthwhile considering using if parking in a dodgy area.
https://www.ebay.com.au/itm/126232624949 (sold out at the moment, but the seller makes them himself, so maybe contact them if interested?).
In the end, nothing will make the car unstealable, all you can really do it make it as difficult as possible.