Whether it's "worth it" to farm IGG (in-game-gold) to buy game-time really depends on two factors:
1) Do you enjoy the time you're generating the gold?
After all, if you're having fun farming, running instances, crafting items, or even playing the Auction House, if you're enjoying it you're already ahead in terms of efficiency of time.
2) Could you be making more money doing something else at that exact moment?
You may make $20/hour at your FT job, but you're probably salaried, or capped on wage-hours. If your alternative to grinding IGG gold at any given moment is that you're able to work for real cash at a higher rate, then it may be better to work rather than game (enjoyment aside). This is not most people's situation though. Most people can't choose to do more work for more money at any given moment; they can only work when they're at work, and thus have a finite cash resource pool. In other words, your leisure time is not worth the same amount as your at-work time.
So yes, if you detest making gold in WoW, AND you are able to trade 1 hour of game-time for 1 hour of work-time at a net positive Gold/hour, then you're better off working outside WoW for your subscription fee.
This post was edited by xTrewfyrex on May 3 2016 04:06pm