Just a short explanation, how they can be read the way I meant. Don't really need to turn it into a discussion about the clarity of those rules, I just wanted to state, that it's not a given how they work or are meant to work from the context, though I initially read them the same way you did.
WizarDru said:
How do you figure that it could be read that way?
From the SRD: " Metamagic rods hold the essence of a metamagic feat but do not change the spell slot of the altered spell. All the rods described here are use-activated (but casting spells in a threatened area still draws an attack of opportunity).
So, they are use-activated. Using them during preparation certainly is use-activated, too. And the text in parantheses could only apply to spontaneous casters for all we know.
Possession of a metamagic rod does not confer the associated feat on the owner, only the ability to use the given feat a specified number of times per day.
So, it only confers the ability to use the feat three times per day, but does not mention a change in applying the feat at all!
A sorcerer still must take a full-round action when using a metamagic rod, just as if using a metamagic feat he possesses."
Which is about the strongest argument for my view, since it implies, that the limits on using metamagic feats still apply, but it is not necessary to mention preparation, since there is no change, but since the rod powers the feat (obviously since no spell levels are added), it could be assumed, that sorcerers do not need to make the necessary modifications to the spell, which results in the full-round action casting time, but this rule specifically says, that they do. Of course, sorcerer just has to be read synonymously for all spontaneous casters, everything else would be kinda silly.
It doesn't seem very reasonable to assume, that a sorcerer, who is already better at applying metamagic than a wizard would suddenly be worse with an item, which helps doing so! Especially when looking at the Quicken metamagic rods.
The individual rods say something like "wielder can
cast an empowered spell thrice per day", which IMHO is the strongest hint at "spontaneous application" even for wizards. But even a spell, which is prepared with a rod (if they work that way) is cast and it would be casting an empowered spell (emphasis in that text is on
empowered, not on
cast, then), so this works either way, really.
The text is simply unclear, but given how much more benefit it would be for prepared casters (better metamagic application is one of the boons of spontaneous casting, which those classes pay a hefty price for already!), I can only really see the other version to work properly and in a balanced way (as balanced as it can get with those powerful rods

).
Bye
Thanee