So I've read up on plenty of posts regarding the respawning of things in the game. Which then I concluded all areas (Main, dungeons, caves, towns, etc) entered at a lower level then 40 are pointless to clear out on a return visit as per the in game week respawn period of all chest, hidden items, carts, corpses, reagents, and so forth (By this I mean you can not clear out all areas for the mere satisfaction of 101% completion, and since the areas level lock upon entry to what your level was no need for going in for low level items). However with the exception of houses the items may be of low level however the question is do these things respawn? If so, are books, letters, keys omitted from this or are only certain books, and letters omitted such as skill books or quest related items?
Example: By this method could one, in retrospect, harvest bookshelves to amass a collection of all Amalur literature? Or could one simply clear out all houses for just a little sanctification of perfection?
P.S. Disregarding the inventory/stash limitations, as this is easily circumvented via killing the vendors to create duplicates of items, such as backpacks, which translates to infinite space.