Spirit Series: Upgrade or Not

Spirit series of weapons has a unique feature that adds respective elemental trait on a normal attack in addition to gradual increase of outgoing damages and respective elemental resistance in accordance with its upgrade level. When Aldo's equipped with Fire Spirit Sword, his normal attack becomes a single enemy Fire slash with some damage bonus.

I have not upgraded nor used either of them except some for a research purpose. The reason is the same as in the case of Cruel Angel's series: other useful weapons already available. Further, I guess most players are short of Git, which was probably spent on upgrading Toto or Otherland equipment, or fishing bait.

I would not recommend using Red Card Keys to Toto Dream Land (VH) only for the purpose of upgrading the Spirit series.*

Name	Type	P.ATK	M.ATK	Bonus I	Bonus II
Fire Spirit Sword		165	20	Fire trait to normal attack + damage bonus	Fire ELEM RSS +15%
Water Spirit Katana		172	29	Water trait to normal attack + damage bonus	Water ELEM RSS +15%
Earth Spirit ax		178	8	Earth trait to normal attack + damage bonus	Earth ELEM RSS +15%
Wind Spirit Lance		165	20	Wind trait to normal attack + damage bonus	Wind ELEM RSS +15%

* In a later version, however, maximum of 30 Psalms for Amy can be used for making and upgrading a specific ability orb (a new feature available at ver. 2.2.0). So it may be reasonable to stick to Toto Dream Land (VH) until you gathers the total of 40 Psalms (inc. 10 for Amy's class change).