You strike as an invisible creature (with a +2 bonus on attack rolls), denying your target any Dexterity bonus to AC. (Blink)
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. (Also Blink)
So, if the opponent wants to completely negate the defensive benefit of Blinking, that opponent needs to both be able to see invisible creatures and be able to hit ethereal creatures.
Do they negate the offensive benefit by simply being able to see invisible creatures? Or do they also need to be able to hit one?