The theory behind MSD (Multiple Spark Discharge) is to provide a short burst of sparks per combustion moment instead of just one spark like a normal ignition. I can't remember if it also amplifies the spark to make it more powerful, that might only possible with a more powerful coil. The burst of sparks enables more complete combustion, reduces the chance of misfires, generally makes the combustion cycle more efficient. Different combinations of combustion chamber design, plug placement, air:fuel ratio, etc. etc. will determine how much an MSD will/won't help you. Ages ago I put an MSD on my buddy's 240Z and it made a pretty noticable difference. Power? Not much, but it ran smoother, idled smoother, and actually did start a little quicker. That's a Nissan six, keep in mind.
With your ACCEL Coil, you're getting pretty hot spark already, so you may notice less of a difference than if you were running a bone stock Ford coil.
Oh yes, as far as it allowing your engine to rev higher, its more like it will help a engine tuned for higher RPM operate more efficiently at high engine speeds. I believe the MSD 6 also has an adjustable rev limiter, enabling you to set it to kick in at the appropriate point for your engine.