Yeah, I've decided to forget about mirror-link units for now, I've not seen any cheap enough.
Admittedly I haven't researched heavily, as I simply don't have enough time...
The XAV-?01BT are Android-based apparently, so I'm sure there's plenty of hack-ability to be had.
When I have better wheels I'll worry about a better carputer/head-unit, & everything that hangs off it.
The DSX-A50BT meets all my basic requirements, & reviews look favorable, for the price.
Although again, I don't have time to compare it against many other similarly priced/specc'd units.
No doubt there's others out there that are similarly priced, but better overall...

*UPDATE* 18/04/13 @420pm AustEST:
Anyone else have some thoughts on the unit I went with? (see post #4)
Would you have picked something different in that (rough) price-range, if so, what?