It from $5 to $10 a few weeks ago because someone thought halving production rate would halve bitcoin offer, but does it really?
According to any logic after halving the production rate the price should double after that (slowly/or not).
Logic says the effect of a reduction of 25 BTC will be undetectable -- there is 10 million BTC in circulation. Also, don't forget that the actual amount of BTC is 21 million. Unmined BTC already exists, but it hasn't be put into circulation yet.
BTC prices depend on supply and demand. If you assume that 10% of mined bitcoins are sold immediately on MtGox, then a drop of 25 BTC in the block reward will cause a 1% drop in the supply of BTC on MtGox. Again, logic says that the effect will be undetectable.
Now, show me your logic.