I think that the benefits of having a forsaken dungeon pass isn't really rewarding. What I mean is that the forsaken dungeon pass quest is difficult (Yes, i know, i completed it) and the rewards / benefits isn't really that great for some reason. 
1.] Yggberries can also be farmed on for_fild02 (soldier) and the soldier mobs is also plenty. 
2.] The usakoring card and others have really cheap value, so even someone without f.dungeon pass can obtain it easily. 
My suggestion is either: 
1.] Make the f.dungeon pass quest alot easier. (not really a good option) 
or 
2.] Have some more drops which is a little rare - medium rare on f.dungeon. Or much better have some random mvp spawn on the f.dungeon every 1 hour. (Must better) 
Those are my thoughts. Anyway, any insights are appreciated =)