The description of the blink spell says, in part:
Physical attacks against you have a 50% miss chance, and the Blind-Fight feat doesn’t help opponents, since you’re ethereal and not merely invisible. If the attack is capable of striking ethereal creatures, the miss chance is only 20% (for concealment).
If the attacker can see invisible creatures, the miss chance is also only 20%. (For an attacker who can both see and strike ethereal creatures, there is no miss chance.) Likewise, your own attacks have a 20% miss chance, since you sometimes go ethereal just as you are about to strike.
You can see ethereal creatures using the see invisibility spell (emphasis mine):
You can see any objects or beings that are invisible within your range of vision, as well as any that are ethereal, as if they were normally visible. Such creatures are visible to you as translucent shapes, allowing you easily to discern the difference between visible, invisible, and ethereal creatures.
However, the relevant part of the description of Spirit Sensing Stance says (emphasis mine):
While in this stance, the initiators gains the scent special ability and he may detect creatures on the Ethereal plane that are near the Material plane within 30-ft. of his position.
If the creature you're attacking is in the Ethereal Plane, does it lower your miss chance from 50% to 20% if you can "detect" it? Or do you specifically need to be able to "see" it, as with see invisibility?