Same flight (YUL-YYC): in front we were offered a choice of either 3000 miles or $75. (I assume it's an MCO.)

Means that AC values the miles at 2.5 cents each. Which arguably is not an unreasonable value for people with status. But also means that Aeroplan is nicely subsidized, since for non-status folks, a mile is clearly worth less than a cent.

In the back they were offered that green piece of paper that directs them to the web site, and they got an e-mail offering the 5% discount code for a next ticket.

So, people in economy who manage to use the discount code on a ticket over $1500 end up doing better...

Anyway, I took the miles and my wife took the cash.