This ratio determines how many basic land cards players will need in their deck in order to cast spell cards for combat and defense when playing a game
They can also be put in your Inkwell if they aren't the card you're looking for at the time
Retreat to Hagra Retreat to Hagra is a great black landfall card, and apart from Ob Nixilis, the Fallen, it may even be the best
Delirium becomes even easier if you can tap this consistently
I would try and address that by ensuring that the copying cannot self-perpetuate that spells are less likely to white copy spells, and creatures less likely to white copy creatures, or that they are reactive or defensive
It works just as well with creatures who have higher base power than toughness, for example, so it could serve as a nice bit of extra damage in aggressive black lists