Theres no such thing as casual gamer in WoW. If you plan to be casual you'll eventually get bored of it very fast cause you will be doing the same stuffs that everyone else is doing

If you dedicate a little more time you will be able to see more endgame content which will eventually lead you and your guild to spend more and more time in it. Theres so many instances for you to clear in a week time and if your guild still in learning process then be prepared to spend countless hours without logging off with an extra epic loot cause a lot of time will be spent on learning and trying out new stuffs

Its either you play hardcore or dont play at all otherwise its a waste of money. I'm sure everyone that plays WoW will tend to be hardcore otherwise you'll be walking around only in Karazhan gears while others will be walking around with SSC/Eye onwards gear

I quitted WoW a long time ago after my guild down Gruul and i felt that my life span increased by twice lol cause now i have more free time to do other things