I think either some cooldown, id say ~1-2min would be fine. The OP suggestion is ok, i would personally suggests a timer and % nerf to efficiency
Pots used:
1st: no trouble
2nd: no trouble yet, but 1m cooldown
3rd: 1.0m cooldown, at 80% (overgulping penalty I)
4th: 1.5m cooldown, at 60% (overgulping pen II)
5th: 2.0m cooldown, at 50% (overgulping pen III)
6th: 2.5m cooldown, at 40% (overgulping pen III)
7th: 3.0m cooldown, at 30% (overgulping pen IV)
8 and on: 25%, 1d3% chance that you get stunned for 1d5 seconds. (mnemonic overkill)
Maybe, just maybe, gearing for max-spellpoins, and managing sp will be important again.
I play Sorcerers and Wizards mostly