The law of supply and demand only applies if the demand increases at a faster rate than the rate at which the supply does -- i.e. the demand remains constant while the supply decreases, or the demand increases while the supply remains constant. The block halving does not constitute a decrease in supply but a decrease in the rate of increase of supply. That would matter if and only if the demand is increasing, which it is not. The demand is very little and almost negligible. If you want to raise the value of a coin, then create a need for it rather than citing economic laws that don't apply to the situation.
This is basically what you're saying, but paraphrased into one sentence. "Doubling the production cost of a certain good or service has no bearing on the price."
In reality, when production costs go up, producers must either ask a higher price for their work, find a way to reduce costs or stop producing.