I've been there... I understand your frustration. This is, at least for me, the worst quest on AG by far.
You can do what you're suggesting and add +2 to each battle trait, but, again, you may not get a talisman fragment at the end and you've just wasted shadow cores. Also, I would only recommend you spending 100 SC on the drop rarity range if you're playing a harder level; in easier levels, well, it may not be worth it.
This is like a lottery and I don't have any good advice for you. I farmed harder fields (with and without battle traits) and nothing... Then I farmed easier fields (less waves, less time wasted, you know) and nothing as well. In the end, I gave up and continued playing (and enjoying) the game. Eventually, I got it, but it took an awfully long time.
Sorry I can't be more useful. You can ask this in the game comments. Maybe somebody has better tips :|
thanks for all the tips @kegaumongo
after 5 days of insanely farming i finally completed the ice cube quest
this is how i did: completed ever single stage i could on glaring, then started farming SC's on J3 (for some reason there are a lot of apparitions and stuff there), and then started playing initial stage with the maximum battle traits i could, i noticed a slightly increase in talisman drop there, but it may be just luck
so good luck to all other quest hunters