1. Which materials are worth stacking? I know you should try to stack materials and sell them when the prices are high, but are all materials really worth keeping, or should I only keep the rare ones? And how do I know if the prices are high or low?
2. How about collector items? Are they worth keeping or should I just sell them without question?
3. Runes. What runes are worth keeping? Should I stack up on those as well?
4. I've got some Scrolls of Rampager's Insight/Adventurer's Insight. Are they worth anything?
5. What about weapons and upgrades? Should I just hold onto weapons/upgrades with max stats or what?
...That's all I can think of at the moment. Any answers would be greatly appreciated, thanks.

