Many people are reporting that the weekend quest, the Library Quests, are not giving increased rewards and have even given people LESS for the amount they've spent on the item (though that could be due to the item rarity and whatnot).
I'll tag the people in question, but I noticed this too. I cannot remember the item exactly, but I purchased it for around 3000 sP and only received 2000 sP in return. I'm not sure if there's a bug or if I'm just overshooting when I purchase things.
Others who have also had the problem: (apologies if you did not want to be pinged, I pinged so you could give your account on what is happening)
The quests are giving out retired books and the special "weekend quest event" books, though, so at least some of the the weekend quest buff thing is apparently in effect and working.
I will agree that there doesn't seem to be a large sP increase from the regular daily quests, from what I saw today, although that may be intentional.
Increased prizes doesn't always mean sP. I got 2 retired books, 5 quest only books and a bunch of super rares.
Dexter by ❤