If more mining rigs use FPGA and ASIC, then those miners will be able to sell for less. So there will be less resistance to a fall in price.
No, miners are always selling for as much as they can, they are not (that) stupid.
Yes, they will look for the highest price. But if the price drops (for other reason) ASIC miners will still be able to have profit. ASIC will not cause price drop, but will reduce resistance to price drop, until everyone has ASIC, difficulty is x500 higher, and mining costs are high again as today.
x500 from
https://en.bitcoin.it/wiki/Mining_hardware_comparison - Mhash/J for GPU is about 2, for ASIC is 1000.
At current difficulty a GPU miner cannot profit if price falls below $5.50, but ASIC miner can profit at $0.02 (this is just electricity cost, ignores hardware cost). Look at
http://bitcoinx.com/profit/index.php, with difficulty=3million, electricity $0.15/kwh, power 1500W with 1500GH/s for ASIC (eg BFL minirig SC) or 3GH/s for 4xGPU.
Good business plan would be - buy BFL ASIC minirig, sell coins at $5, force GPU miners to quit. From
http://bitcoinx.com/profit/index.php you profit $40000 in 1 month - time to buy another BFL ASIC. But difficulty might reduce from GPU miners quitting, so maybe you profit even more. Or maybe you cause crash in bitcoin and lose everything :-)
Biggest problem: do BFL really have 1.5TH/J hardware for $30k?