Gut reaction? No.
Make it spell level specific and maybe, if the price is scaled to advance geometrically. And, like all magic items, you can't "stack" effects by consuming several, even if they are for different spell levels.
Also, perhaps limit it to prepared casters? I mean it's not like a Sorcerer or Bard can "cram" to memorize additional spells.
Maybe add a "hangover" effect that sharply cuts the number of spells that can be prepared the day after its use, instead of doing the "Deadly poison". There are, after all, ways to be poison immune and you know that people will go there as fast as a Munchkin can run.
Acknowledging that characters get richer as they advance in levels, and acknowledging that the number of spells a caster can have (and thus double with the potion) increases as well, this potion would be a must-have for every spell caster of every class at higher levels. (Okay, maybe not Paladins or Rangers, since they aren't primarily spell casters, but you know what I mean.)
