In a 2 player game, you do NOT have to go up the obelisk one side at a time...I could accrue crystals, then swoop in, buy 1 7 offering, then sit there next turn and snap up the other 7, right?
How does this work in 4 player? I imagine people just spending all over the obelisk, whereever they can find open spaces...
I can't think of any reason why a player wouldn't always buy the cheapest spot(s) available. Saves crystals for later, makes it more expensive for the other players.
If crystals were face up, you might conspire to stop a player from winning, which might require one of the other players "skipping" a spot so a less fortunate player could afford to fill it, thereby stopping a third player, but I don't think I'd play with people who did that again.