I think I'm going to have to concede the argument. Claws of the Beast has a spell effect that is variable and numeric, and so it is empowerable.
I'm still not convinced, and I'm about to try at length to unconvince you as well.
The summary
The effect of the power is (claws which deal 1d4 damage.) The damage range (1d4) is a property of the claws, and is not itself variable.
The argument:
One way to read the power is that, at the moment of casting, you roll a d4, and that's how much damage the claws do with each attack. That is not how anyone I know would play it.
Yet there is nothing in the specific language of the power that makes this clear. The reason no one plays this way is that they already implicitly understand what a damage roll associated with an attack means: every time you attack, you roll that particular combination of dice to find the base damage dealt.
Hyp mentioned that he doesn't like using common sense as a rule in this case. But here, we're already using our common sense to make a judgment on what "claws ... dealing 1d4 damage" actually means.
Once you've made that judgment, the "1d4 damage" bit ceases to be a variable, numeric effect of the power. Despite the fact that it
is a numerical range mentioned in the power's description (and not directly referred to elsewhere in the rules), it is
not parsed as a direct effect of the power. Rather, we have understood the claws as weapons which deal a certain dice range of damage, in exactly the same way we would have read a spell which created "a dagger dealing 1d4 damage." And as with the dagger, we know that the die specified is not itself a variable numeric effect, but rather a damage range which the claws themselves posess.
Hyp''s rule of thumb would argue that in the case of a spell creating a dagger, because the damage dealt by a dagger is specified elsewhere in the rules, we know it not to be an effect of the spell.
I am arguing that, implicit in how most people would parse
claws of the beast, we understand the damage range in exactly the same way. We have categorized the claws as a weapon with a particular damage range, and inherent in
that categorization is the categorization of the damage range as a property of the weapon in question. Despite the fact that this particular weapon is not mentioned elsewhere in the rules, we have extrapolated the behavior of the claws from our knowledge of how other weapons function. The damage range of the claws exists in the broader framework of the rules, and in that framework the damage dealt by any one attack is
not an effect of the spell. Rather, it is the
damage range itself which is the effect, and this range is not variable.
Now, if you roll the 1d4 when the power was manifested, and have the claws deal exactly that much damage with each attack,
then I would agree that the claws could be empowered/maximized/whatever. Anyone been playing it this way? ^_^