Well, I could be wrong here, but for literacy the main gpal is to not increase your rate of research but to hit the levels of literacy at which your pops will start promoting to the industrial classes easily. I for bonus craftsman promotion a pop group needs 40% literacy, while for clerks 60% literacy is needed. This is the literacy rate of specific pops, rather than the literacy of your state, which can be found in the population tab.
As for the techs, the literacy tech tree is all about getting that Darwinism invention, which unlocks off of the 1850 tech. Basically, if you're not going to hit 40% literacy by 1850, I would consider rushed that tech, as there aren't any real competitors for 1850 tech unless you really want Nationalism & Imperialism. For France, Britain and Prussia, you can probably neglect the literacy tree. For Russia, the Ottomans and Austria, the literacy techs are probably needed if you wish to compete industrially.