So coming up in my campaign, I needed a good excuse to have a magical item become much more powerful than normal. Like powerful enough to place a curse on an entire town just by being present. The solution I came up with was to have the item's location be on the intersection of magical ley lines. In this context, ley lines would essentially be magical fields (kind of like Earth's magnetic field) that span the land providing the magical energy required for spell casting. Areas where they intersect would be intensely magical.

Mechanically, I'm going to essentially turn all my Spellcasters into Wild Magic Sorcerers temporarily. When they cast a spell, I'll have them roll a die. If the result is <= [Spell Level] the spell gets the effect of Empowered Metamagic (reroll 1s and 2s on damage) and the player rolls on wild magic table.

As they get closer to the center of the juncture, the change of the effect increases by lowering the die they roll. In town they roll a d20, in the crypt built on top of the junction they roll d12, in the main chamber of the crypt they roll d6, within 10 feet of the dais the super powered magic item is resting on they roll a d4, if they are on the 10 ft dais they automatically get the effect.

I only have two real casters in my party of sixish, a wizard and a cleric (I know, I know, Arcane vs. Divine. But I'm going to say the ley lines produce such a powerful disruption it even warps divine magic). Hopefully the effect balances well enough that they will have to put some thought into whether the effect of the spell is worth the possibility of a magical mishap. The Wizard is pretty chaotic and will probably just go nuts trying to set off the effect, and the Cleric is more cautious and I predict will start holding back his casting to avoid the chaos.

My question to you is whether you think this mechanic is just going to be mildly broken and slightly zany or stupidly broken and cause the game to come to a grinding halt. Any input?