First of all, DMP is the 1% spenders within the DM cohort. With the amount of flying on CX metal, OP should be writing a guide instead of asking questions.

Logically it makes no sense for people to buy a shiny card. If you are flying a lot then you'll earn GO/DM organically. If you rarely fly, you've just spent hundreds if not thousands just for a shot at upgrades/ priority food/ DYKWIA. Even for the first-class lounge, I don't think the cabanas or the oven-reheated food is worth the risk of being banished by CX.