Do you think it’s worth buying for all accounts or just wait till you’ve farmed the gold?

i just started multi-boxing - my main goal is to pay for shadowlands / monthly sub for 5 accounts all through gold.
Currently doing transmog runs... it makes gold but so slow., not sure if upgrading to bfa would allow me to farm more effiecntly to make it worth it?

idealistically I’d like to get to a point where I can pay for subs and then some extra for upgrades by only farming 1-2 hours avg per day.