How do non-spell powers work with Wizard preparation? Say, for example, I made a Tiefling Wizard with the Grim Isolation racial daily power — how would this work with regards to choosing my abilities each day? Would I pretend that Grim Isolation was a spell and choose between it and that level's other daily like normal, or would I always have access to it independent of the usual Wizard daily pick process?
Wizards of both the Mage and Arcanist stripe get to choose two utility spells at typical utility levels (2, 6, 10 etc). You can prepare one of each slot each day.
Daily and Utility Powers: Your spellbook also holds your wizard daily attack powers and wizard utility powers (not including your cantrips). You begin with two daily attack powers in your spellbook, one of which you can use on any given day. Each time you gain a level that lets you select a wizard daily attack power or a wizard utility power, choose two different powers of that type at that level and add them to your book.
However, if they choose to select non-wizard utilities, like the Tiefling racial utility Grim Isolation that you mention, they only get to select it and always have it prepared. The mage's language is less specific than the Arcanist, but I'm still not seeing a clear case where DDI's character builder is in the right here. It reads to me that if you take a wizard power you can take a second one, but if you take a racial power you can't take another spell.