Takes me 40 points to get 3 experience books at the start and then the prizes are getting better as you go. But once you get all the girl's shards it takes way more points to get to the next stage and the prizes are worse.
Example Path of Valor:
490 to 560 (70 points) net you 4 books
560 to 640 (80 points) nets you 5 books
1000 to 1100 (100 points) nets you 6 books
1600 to 1700 (100 points) nets you 8 books
1700 to 1800 (100 points) nets you 10 books
2500 to 2750 (250 points) nets you 4 books
Does seems like the work after that is meaningless even for developers. Once you get the last shards at 2100 seems deflated value, but increase work to get them.