… to me it seems that one dispel is easier to remember / manage than all the little cures you propose. The spell-book is loaded already like it is so one dispel that fits all sounds more manageable.
As for creature growth spell… that could be a nice spell. If restricted in some way… like make it level 4+ or make it cost tons of mana, or make it SP dependent.
It is a much more complex system what you are proposing. I think it would be better suited to heroes 7, or a heavy h3 mod that remakes the skill system aswel to look more like h5 (some of the spells you propose could be moved to secondary skills)