As I've said, I agree that it's probably RAI that Rage Mage be qualified for with "second level or higher", but strictly speaking the level of a spell is a measure of a non-divisible trait it possesses. The text TML found doesn't deny this; instead the argument he is making is that the flavor text suggests that higher-level spells should be adequate for the purpose. In terms of the coins-and-screws analogy, he is essentially asking "well, is it that bad if we use a 15mm screw and it sticks out a bit?"
For the record, I think RAW is a useless concept. It's contrasted w/ Rules as Intended, which is a separate kettle of fish, but RAW itself still involves heavy interpretation, as all language does, especially all rules do. That's why the IRS is so large.
But, I still think the screws thing is weak. Moreover, it is unclear to me why divisibility is a relevant concept. The screws analogy, the way you want to use it, implies that there is no relevant connection between a 4th level and a 5th level spell. But, everything in D&D is premised on there being such a connection, namely that a 5th level spell is more powerful (complex, etc.) than a 4th level one. This relationship between levels is hardwired in D&D's DNA.
A prerequisite has to be tracking something, and what it is tracking is a character's abilities. So, if a character is able to do something of complexity X, then it seems she should be perfectly capable of doing something less complex than X. That's part of that power and complexity relationship.
I'm going to reiterate an earlier question, though. This point seems, frankly, obvious to me. Is there anyone who as a DM wouldn't let it fly?
