There's definitely nothing that useful in Ohara's library, or someone would have found it by now.
I don't believe there's any mcguffin ĥidden there, and that its value is more abstract.
If that was the case, then why did the WG make a big deal of Ohara researching what they considered forbidden information, along with Oda making a big deal of Clover being killed JUST before he said the name of the great kingdom, which he claimed was a thing where the very name was something that could make the WG shit bricks? Also, along with the fact that they're scattered around the world, it's been mentioned several times that the poneglyphs were written in a language that almost nobody can interpret, and Robin was hounded because she's one of the few who can, which is why the WG put a huge bounty on her. Which explains why nobody else has found out what Ohara was looking for.
As for Ohara itself, it was assumed for ages that the library and its contents were completely destroyed, so there'd be nothing to find. The whole thing about Ohara is just like The One Piece and the treasure of Mary Goeis: it's not what it is, it's what somebody can do with it...which is practically what a MacGuffin is.
And the only reason why we don't know what exactly it is in Ohara's library that is supposed to be found is because we have yet to figure out how Luffy will passively be at the center of that which is to be found because he will never give enough of a shit about it to go along with somebody else's plan if it doesn't help him and what he wants to do.
For Robin, its the emotional connection to her mother and the legacy of her people. To Elbaf, its likely just "knowledge is its own reward."
That's probably what it is on a fundamental level. But again, there's still the fact the WG makes a big deal of going after it, along with things like it, to the point where the Gorosei and now the God's Knights go to great lengths to ensure total destruction. And again, it's all about what can and would be done with what is possessed that creates the value. Assuming that one cares enough about it.