Thanks, guys.
I've checked prices of diamond grinding cups and concrete / masonry grinding wheels. The cups are very expensive. The wheels, not so much. For example:
https://www.lowes.ca/grinding-polish..._g1198226.html
or
https://www.lowes.ca/grinding-polish..._g1198210.html
They have good reviews and I'm almost certain one will last long enough to grind down what little area has to be leveled.
Because I had to run someone to the airport this morning, I've yet to call a tool place to see about an adapter for our sander / polisher, but here's an example of an inexpensive 6A, 4-1/2" grinder:
4-1/2 in. Angle Grinder | Princess Auto
So, for the cost of a rental, I could have a new tool (that I need like a hole in the head) and a grinding disk.
But for this one simple, quick job, I was hoping to get an even less expensive adapter for our 11A sander and install one of the above concrete grinding disks.
Regardless of which tool I end up using, because of the certainty of a lot of dust, this will be a two-person operation. My wife will hold the large-diameter hose of our hearing-destroying shop-vac (that sucks like the black hole at the center of our galaxy) right where the disk will grind and eject the concrete. If the hose is kept close to the contact point, this should reduce the dust to a bare minimum. (Add this to the list of Famous Last Words.) Just to be safe, I'll move our Outlander and Z out of the garage and down the street some safe distance from any potential dust.
Thanks again, folks.