Walter:Advanced Plus is no longer a class. Once upon a time, PADI offered it as an option to their AOW course. It included more dives (9 if memory serves) and actual academics. It was a fairly good advanced course, but since it didn't produce enough revenue, they axed it.
When I first became a PADI instructor the Advanced plus course was still around. I'd have to look back though old instructor manuals to find the standards but if I remember right (and I may not) the academics were exactly the same as the DM course only without the testing requirements. And, yes, I believe there were more dives.
I'm sure lack of sales was the reason for doing away with the course but you have to wonder why there was a lack of sales. It's not too uncommon for charters to require AOW for access to certain dives. My opinion is that divers and shops only do what is required for access. I think it's a shame that divers don't enjoy learning and instructors don't enjoy teaching, diving related things like decompression theory, dive physics, physiology, dive equipment ect.
Time to stop refering to this sport as diving and start calling it underwater tourism.