The four basic laws of supply and demand are:
If demand increases and supply remains unchanged, then it leads to higher equilibrium price and higher quantity
If demand decreases and supply remains unchanged, then it leads to lower equilibrium price and lower quantity.
If demand remains unchanged and supply increases, then it leads to lower equilibrium price and higher quantity.
If demand remains unchanged and supply decreases, then it leads to higher equilibrium price and lower quantity.
Now the big questions to answer are "What will happen with demand" and "What will happen with supply".
At first glance it looks like that due to the decrease of the block level award the supply of BTC will be halved. At the same time there are no signals that demand will change. You could argue that demand goes up, as more and more entrants get into the market to try out the Bitcoin ecosystem. Some will conclude that prices will go up.
However supply is not only determined by the amount of newly created BTC's. We still have a stock of 10 million BTC's. It is fair to say that 80% of these BTC's are hoarded. There is unfortunately still no real economy based on BTC's. They are not commonly used to pay salaries and pay bills of suppliers. All the ASIC suppliers quote and invoice their Asics in US$ (and yes, you could buy them in BTC as well). As long as even the larger players do pay their suppliers, investors, tax bills and employees in fiat currencies it is fair to assume that we have a overhang stock of at least 8 million BTC. Of course people will argue that MTGOX is trading 50.000 BTC/day. Yes, true, but this is nothing else of transferring BTC from one hoarding wallet to another one.
Once pricing goes up, more and more of these speculative BTC will come on the market, driving prices immediately down. My simple conclusion is that demand is going slightly up, supply remains the same, pricing of Bitcoin will raise slowly.
Now what will happen after all these ASICs comes on board of the Bitcoin network. Well, something interesting will happen. Total demand will again slightly improve. Supply will remain the same at 3600BTC/day plus supply from "stock". So nothing structural will change.
There will be at least 15.000 ASICs on the market, assuming three manufacturers will eventually get there, each of them at least supplying 5000 ASICs. With 3600 BTC/day available, this will give each of the ASIC 0.24 BTC per day, at today's BTC pricing something like $3/day/ASIC.
At the moment these ASICs comes at the doorstep of a miner they have a limited time to cash. The resale value will be zero, as these ASICs do not have an alternative use (may be a heating device for a cup of t). This means you have to fully write them off at once. To get any ROI these miners can do two things: Speculate (and hoard) or sell their Bitcoins asap. Hoarding doesn't guarantee a ROI, so they will have to start selling their Bitcoins.
The minimum price they want to see for their BTC's is at least the price which covers their variable costs (Their electricity bill). Everything above this price will support their write-off and the time they are devoting to the project. With the power consumption of 50W per ASIC you will get a electricity bill of 1.2 KWh per day. This will be the minimum price per ASIC. By 15.000 ASIC's, each ASIC in average gets 0.24BTC, so 1 BTC will have a variable costs of 5KwH/day. Say 1 KwH costs you 0.2$, it is fair to say that the variable costs will be $1/BTC. This will be the case until new technology with a higher efficiency will get into the market.
Now with 15.000 ASICS in the market, an unlimited amount of more ASICs able to enter the market, electricity bills to be paid and a "hangover" stock of more than 10 million BTC's miners are forced to sell. This will drive prices down to $1/BTC, as soon as ASICs will be connected to the Bitcoin network.