Having never flown up there, how hard is it to get a clearance off the Amberley mob?
Depends, on what they've got going on. They're generally a helpful mob.
For a VFR pilot, their airspace can be complex and intimidating. The terrain in that area is pretty intimidating as well if you're trying to get from the west to the eastern side of the range. There is lots of gotcha terrain as well, places where you think you can get through. It's just not the type of terrain you want to be messing around with in low vis and cloud.
It's pretty simple getting over the range, if you're IFR.