I spent a while at Sorell recently, mainly at the Waterview Sanctua
Probably the major users of boxthorns here are those other imports, House Sparrows
I've noted elsewhere, that the House Sparrows use them for what I call their 'castles'. Close to where I live in Bellerive the main predator of the House Sparrow is the Grey Butcherbird. If the sparrows are being harried by them, they take cover in these very effective refuges.
So while I'm certainly not advocating keeping or planting boxthorns, there can at times be an upside to them! I should hasten to add that I don't include their use as 'castles' for the sparrows as an upside.
[Images are of New Holland Honeyeater and Superb Fairy-wren, both photographed on boxthorn, at Sorell.]