From launch I harvested 977 blocks getting 13208 XEM

so it is about 13.5 xem a block, not much if u do 3-4 blocks a day

It depends on what kind & amount of transactions are included in each block.

I've had multiple 1000+ XEM blocks harvested since I started ...

is the vented coins comes to zero after u generate the block?

and this is my first block worth 0.00 xem
Block #246748 Sep 18, 2015 21:47:27 62.50% 0.00

yes many times the block is 0 ... the more transactions that happen in the network the less chance it will be 0

that sucks,, maybe if there would be some faucets or games, wich use xem that would improve

There is a faucet. Some games are in the works from what I hear.

faucet.nem.io