An advanced AP making $70k teaching 3/3 at the normal 40/40/20% position is earning about $4500 per course taught. Paying a less qualified adjunct more than that is simply not realistic.
An adjunct making $4k/course would earn $32k/year teaching a 4/4, with no research or service expectations, and summer and holiday breaks off. Not bad for a part time position for people who are probably less qualified than the regular TT faculty.
The fix isn't too pay adjuncts more, it's to hire more TT or lecturers and make the current adjuncts more likely to be totally unemployed. Ajuncting should be used for practitioners and retirees with real world experience, not MAs, ABDs, and PhDs who can't land a full time gig.
of course the point is to make universities open up more TT lines or even lecturer positions. I don't see a way of doing that unless we can make adjuncting too expensive.
keep in mind that your advanced AP probably has input on what classes they teach, when they teach them, etc. The AP might also have a TA. The AP also has a regular salary, as opposed to a semester by semester scramble for classes.
I'll never understand the anti-adjunct sentiment on here. More full time jobs is better for all of us, even if you think that the adjuncts in your department are losers.