The experience points awarded for each Orb that you pick up is based on how many Orbs you have already collected.

Hint Orbs
1: 5,000 each
10: 7,500 each (and 10,000 bonus)
15: 12,500 each (and 25,000 bonus)
35: 15,000 each (and 50,000 bonus)

Landmark Orbs
1: 2,600 each
10: 5,000 each (and 10,000 bonus)
25: 9,750 each (and 25,000 bonus)
100: 15,000 each (and 50,000 bonus)
125: 17, 250 each (and 60,000 bonus)
150: 20,000 each (and 70,000 bonus)