Well, I was mainly thinking of WHMs, as they only have to worry about Korin. On the other hand, Hyorin and Rairin are more than enough for nukers. I only have 4, Korin, Hyorin, Rairin and Furin for Aero V, and don't usually miss the others.

Obis are much easier than completing a +2 magian staff, and provide similar/better bonuses.