I am also having a feeling that the block reward halving will have a near-Zero impact on the Bitcoin prices. On the other hand, it can have a negative effect on it. That is because, a number of short-traders have started accumulating the coins, hoping that the prices will go up due to the halving. If their expectations are not met, they are going to dump their coins, which will drive down the BTC prices.
For the next block halving, from 25 to 12.5 will big effect. For the future ones, like from 12.5 to 6.25 will have much less effect as the proportion of new coin is much smaller.
the 2020 halving will still have some effect, but the 2024 and espcially the 2028 halving will be negligeable