An update after running the nodes for about 11days on mainnet v1.0.4 (except The RPi3 or Raspberry Pi 3, which is more like 7 days):
As you can see, more RelayMessageCount in general leads to more mining rewards. For example DO-1click8, which relayed the largest amount of messages (60,326) and get most mining rewards (17 blocks). RPi3 relayed the second smallest amount of messages (4,789) over 7 days, and yields zero mining reward.
But over this period, there are still lots of variations. For example, AWS-OR2 relayed the smallest amount of messages (4,765) but actually got 4 mining rewards which is about average.
The morale of the story? My sampling size is just too small compared to the total amount of nodes, and my time frame is not that long.