While I agree with your analysis that a shorter cool-down cycle implies weaker powers, if you want to keep things balanced, I have to disagree with your characterization of Vancian magic as any magic with such a cool-down cycle.If you get down to the mechanics, 'Vancian' magic is basically nothing more than powers on a cool down cycle. To me, it's still Vancian magic if you can use the powers 1/encounter or 1/round or 1/game session or 1/x number of seconds as in World or Warcraft or whatever. However, the shorter the cool down cycle, the weaker you have to make the powers to keep it balanced and interesting.
The key element of Vancian magic is that you must prepare specific spells ahead of time. In a Vancian system, magical energy isn't fungible. The spells you prepared earlier -- and have not used yet! -- are the spells you have available -- not the spells you know. If you want to cast two fireballs, prepare two fireballs.
Anyway, if you like the idea of a longer cool-down cycle, I recommend looking at GURPS's Unlimited Mana variant. The standard GURPS magic system is one of the quick-cycle systems you decry, so the designer of the Unlimited Mana introduced two important changes: (1) spellcasters get far more spell points for casting, but those spell points do not recover overnight, and (2) it's not a hard limit, but a soft one, with consequences for using too much power.