Given that the one that fetched $1.2 million was only rated as a near-mint 7.0, previous cards rated higher could wind up being auctioned off at an even higher price later on
let me start off by saying this is in no means an official guide to anything
Unfortunately that was not the case: Seth and Richard are expert gaslighters at our table and managed to convince the group that my Tamiyo with a Shadowspear and Keen Sense, aka a flyer that draws a card, gains 1 life, and makes a clue each turn was an avengers-level threat, so I got swatted like a fly and Omnath predictably did Omnath things
Marvo's slow because you can only do that once per turn, but thats where synergies with Clones and myriad can come into play
Second, some people just like to collect things
Develop and ramp your mana base to play your planeswalkers quickly and efficiently