Effects of Magic on the Real World

One of the major issues I have associated with fantasy settings is that a world filled with magic is essentially medieval plus wizards. It seems even more silly in the context that many settings purport to be thousands of years old. So, what I want to do is make a basic game that could help model the effects magic on an otherwise realistic world.

Originally, I was thinking about setting this up in the ancient / dark ages since my interest is primary on the fantasy realm. Player knowledge would become a significant hindrance though. Effectively players would have unfair knowledge about technological development that could be leveraged with magic. In order to deal with the problem, the game should likely be set in modern day.

I am thinking of setting up a small self contained scenario for this, kind of like Lady Blackbird, with pregens. I want to keep the characters disassociated from the players in order to avoid weirdness. The scenario would kick off when the group uncovered a set of “items of power.” That essentially give those in possession of the items the ability to wield magic. Magic should not be limited in functionality, other than the final result of the effects cannot create paradoxes.

The question becomes, how to model the interaction of magic within the world. I’m thinking a basic die mechanism that can be used to measure the degree of success when attempting to use magic for something. And, while the player always succeeds, their margin of success determines the level of complication created by the act. Complications would scale relative to the effect desired.

As far as complications are concerned, I am thinking about creating some tables that could be rolled against in order to generate some ideas. But, complications that are directly relevant would be preferred. The trick of the matter is trying to figure out how something like, an unlimited supply of free gasoline would affect the world.

What would be the best way to model such a thing?