Cost aside - it's my opinion that VA would benefit significantly from joining Star. They would need to re-align Velocity slightly so that deep discount economy passengers are not penalised (like they currently are).
Unfortunately the alliance ship has sailed, but agree with you here. As the alliances are such a construct of the US carriers, it could never happen, but shame that VA couldn't operate within star (with respect to DL and UA) like QF does within oneworld (with respect to EK and QR). Cosy with non-alliance partner, and almost hostile to the alliance partner, but it seems to work. Star would have to be the choice over Skyteam, SQ alone has more flights to/from Australia than Skyteam, and even without NZ, #*a flights >2x#Skyteam flights.
Also a shame NZ signed the deal with QF, as with Luxon going from NZ within the month, and JB gone from VA, there might have been a chance between two new CEOs. Or maybe not.