Of course, my experience of D&D players is that, when it comes to D&D, most don't actually want to have risk added to their spell casting (check the lack of popularity for the Wild Mage for evidence).
This is a bad example. The wild mage is an absurd design that takes marginal benefit for massive risk, when every other class has nothing similar.
And while you say there is no opportunity cost, I don't find that to be correct - to gain anything magical, something else is not being gained.
You missed my point. I didn't said gaining a magic item didn't have opportunity cost, I said using one didn't. There's a big difference.