Though to be fair, much of the changes in Ravenloft are horrific to foreigners (and players unfamiliar with the changes) but not as effective on natives. A native caster might not know why certain spells don't work, but they know they don't. And while Ravenloft isn't very big on mage guilds and schools, the notion that divination is unreliable, conjuration rarely works right, and necromancy is corrupting would probably be heard about.
Long story short, I find the corruption of spells fun for a few sessions before it gets tedious.