Honestly, 4 player play pretty much requires two of the box game to be feasible.
Not even just for the status boards..
You need more dice, more counters, another set of quickcast markers, damage/mana tokens, more copies of key spells, and more copies of the mage cards incase more than one person wants to use the same type of mage. (and more copies of things to support that, such as voltaric shield tokens, pet token, etc)
Ive done a lot of 4 player games, and trying to squeeze 1 core game to acommodate that many people is a really tough. Especially if the players want to branch out and customize their books.