I've noticed something. When it comes to my bookish friends, a lot of them are total Elinors. They'd own every book in the world if they could, and it doesn't even really matter to them if they read them all.
Now, let's think about Capricorn. From what we know at this point, the only reason he wants that mysterious book Mo has so badly is because it's powerful. Not because of the real value of the story (hypothetical) inside, and not because of anything but its non-literary value.
Compare those two people, and we have a very odd similarity. Sure, Elinor appreciates the actual words a lot more than Capricorn ever could, but they both seem to have this same weird value complex. They hold books up as books themselves, objects of power, not as stories.
This is probably one of the reasons we, as a literary society, hold classics up and constantly praise them, even if their actual stories are absolute, badly-written shit. Classics are not stories of value, they are important because they are powerful. Because they influenced, because they were widely read, and most importantly, because they are old.
That is a very key detail, because that is why Elinor cares so much about her most "valuable" books. They're not her favorites, they're not sad or incredible or fantastic. They're old. They're expensive.
She protects her "inky children" because they are simply her collection of valuable material objects, not because they are a collection of stories.
I may argue that this, not Meggie's age, is why she and Meggie don't inherently get along. Meggie takes comfort in all of the words of a book, she sinks herself into the stories, and lets herself love stories and consume them as media and as an imaginative art form rather than a thing of material value.
This is the same with Mo, evidenced by how they scatter books all over their house, why Meggie sleeps with one under her pillow, why she's constantly talking about the comfort of books and their stories rather than the comfort of books and their value.
As it turns out, people in this universe have it all wrong. Only because books are worth so much, only because they have so much power, are they cared for.
Think about it for yourself. The original Inkheart, the one in the story, isn't praised for how good it is or how beautiful the world is, or any of that junk. It's sought after and chased because is has material power. Because it is the very fabric of the existence of this universe's power, because it is magic.
But the story? You don't hear shit about that.
Well, not from anyone other than Meggie.
And, hey, maybe Elinor's thoughts about books are a little bit exaggerated for a reason. The world's level of importance placed upon books for things other than the amazing stories they tell is precisely why this drama exists. It probably would have been less obvious if Elinor's personality had been dialed down to what it is like in today's book nerds, but the point still stands.
Now, if people could just read, enjoy the damn book, not fuss over it, and value the things it contains rather than what it is or what it does, I doubt a) that Elinor would have spent as much pointless money on books, b) that Meggie would ever be in significant danger, at all, and c)that all the corruption involving books revealed later in the series would have ever been a problem.
After all, the beautiful covers and fonts and ribbon bookmarks are only shells. The real value is in the little world itself, the one that has nothing to do with the publisher, nor the cover, nor the edition, nor the age.
Don't judge a book by its cover, indeed.