I think playing around with the spells is a good idea, in particular buffing Sleep, Dispel and Slow, as well as Blast. I do have to question giving (additional) spells to characters such as Bowie, Slade, Eric and Randolf, however. Both Bowie and Slade are already really powerful as they are, if anything they should be made weaker and not stronger. A Centaur with already high HP, Def and Movement doesn't seem to be a good candidate for receiving powerful wizard spells. Giving Randolf the status effects spells is more or less fine as they're shitty anyway.
I do have to say that the idea of an MP-recovering AoE spell is quite cool, in particular as it hasn't been done before - but I'd suggest giving it to a Domingo-style character, for example by nerfing Peter's ATT & DEF to the ground and make him some sort of caster/MP recharging station hybrid.
To me, it kinda sounds like you want to hand out cool stuff without really thinking about the implications. If you create an Eric with access to level 3 of Freeze/Blaze/Bolt while he retains his original ATT/HP/DEF/MOV stats, he is bound to put the wizards out of business. You're not really improving the gaming experience there, as instead of having the choice between two characters (a KNTE or a MAGE) there is only one option left, as Eric is clearly superior.
As such, my primary suggestion is: if you're giving something to a character, always take something away as well. If you for example want to have a centaur wizard, make his attack and/or defense weak.