Its so ubiquitous that its banned in every format except Commander (its a key piece in the best Commander decks) and Vintage, where its restricted to just one copy
Much of the advice will hold true for other MTG formats as well, but if you're working on an EDH deck, our guide to how to build a Commander deck has more specific advice for you
6 Steel Wall and Perimeter Captain 1-drop Walls are among the best you can acquire in Magic
Yavimaya, Cradle of Growth: A high value land, which helps mana fixing a lot by turning everything into forests
Wizards opens up a purchase window on their Secret Lair site that usually lasts for quite a while when a Lair drops, generally about a month
Regardless of the reason, the point of all this is that casual staples are likely to lose less value over the next couple of months than the new cards and more tournament-focused reprints