In a nutshell - yes they should, but do they need to? No, not really. JB seems to have built up a fairly good network of partners, however, there are still a few major black-spots, including continental Europe, Africa, and Northern Asia (maybe ANA or a Chinese carrier).
If they don't want to join *A then at least make the benefits between airlines clearer, including baggage allowances and priority benefits. The lounge access seems to be all over the place. I see that both *A and OW have thier anomolies, but consider these scenarios:
* Flying to SYD-HKG on VS - no SYD lounge access as it is a VS partner lounge
* Flying SFO-SYD on NZ - no SFO lounge access as NZ does not own the lounge
* Flying STD-DPS on DJ - no facilities available at SYD for DJ passengers
A VA elite should be able to access the operating carriers (VS) lounge at the port (NZ for SYD). Sure, make VA pay for it, but lounge access at one end (HKG) and not the other (SYD) does not make any sense
I know there are rules with 'partner lounges', but these are key citites (maybe not DPS

) that VA should be encouraging elites to travel with their partner airlines on. In contrast, a QF elite travelling on BA can access a CX lounge. VA need to pick up their game in this respect.