How much mileage is expected?

[Qwerty321]

I've got a BA Fairlane with 420,000 kms on the clock right now and apart from needing new coil packs, she's pretty much running in perfect shape. There are a couple telltale signs of aging though, for example the RHF door wiring loom is shot so I get no sound from that speaker and when closing the door (particularly hard - long story), my mate ripped the entire left door handle off (I've reattached with a lot of superglue for now, hopefully it'll hold).

The thing I find fascinating with this car is the fact the engine numbers match, and it looks pretty much bog standard. There's no external tranny cooler fitted, so I'm going to assume the transmission in there is the original as well (surely if you did work on the transmission you'd fit an external cooler).

Anyway, at what point do these cars actually give out? I got my fairlane pretty cheap and I do like it quite a lot, but I'm considering whether I should bother maintaining it (new coil packs, servicing it properly, fitting external cooler etc.) or should I just run her till she dies, not spend a dime on her, and just buy a BF Falcon with say 150,000 on the clock once the fairlane conks out. That said, if I could expect the fairlane to keep running into the 600,000's then I'll prefer to put in the preventative maintenance and keep her going.