Currently things work as follows:
- The VP reward boat comes at midnight UTC
- The highest point your VPs reached during the previous 24 hours (from the time the boat arrives minus 24 hours) determines how big your VP reward options will be
- The game rolls separately for each of your three options
The chances for each option are:
Diamonds - 20%
Resources - 40%
Power Stones - 40%
If Resources win another roll is made:
Gold - 25%
Wood - 25%
Stone - 25%
Iron - 25%
If Resources are chosen, the quantity scales upwards in a very linear fashion with each additional VP you gain.
If Diamonds are chosen the quantity scales roughly as follows:
However, the Power Stone reward has some clear cutoff points due to the value of a Power Stone Crystal.
For the future:
Currently the Power Stone reward thresholds are quite blunt - at ~700 VPs you can be offered a Power Stone Crystal and then you won't be offered a second Crystal until ~1,080 VPs. We're going to smooth this transition out in the next update by changing all of the Power Stone rewards to be either Fragments or Shards.
Therefore, at ~700 VPs you can be offered 7 Shards instead of a Crystal and so on. This graph will explain the rest: