I really don't see the point in spell rank. The only purpose it seems to serve is to duplicate the function of spell prerequisites (as pointed out earlier in this forum). Rank is explained as denoting "how complex and powerful" spells are, but again its only purpose seems to be to indicate that it should have a spell of one rank lower as a prerequisite. If that is truly the only purpose, then I'd suggest eliminating rank since it is less useful than the information listed under prerequisites. Then, the rules simply need to state that a beginning mage starts the game with basic spells only (those that have no prerequisites).
If rank truly measures the complexity of a spell, then that complexity should be reflected in making the spell more difficult to learn (e.g., rank penalty to the INT or LANGUAGES check) and more difficult to cast (e.g., rank penalty to the skill check). As the rules are right now, it is no more challenging for a mage to cast a rank 5 spell than a rank 1 spell.