to second parsifal, suvarnabhumi is about 30 to 60 mins from downtown bangkok. KLIA and KLCCT are abt 30-40 mins by train and 60 mins by bus/car from downtown Kuala Lumpur. i agree that Clark should have been ideal to serve Manila as the distance to NAIA (about 100kms one way) is comparable to the set up in other ASEAN countries.
however i'd like to emphasize that the only time Clark will be feasible is if there is a fast link from Clark to Manila, such as a train link. on my last visit i found that with the impressive new NLEX, you can go from Clark to north manila in about 40 mins, so im pretty sure a train link extending from a central station in, say, makati, will do the job. however if parsifal's suggestion to make NAIA the domestic hub is adopted, then that means it should be a terminal-to-terminal link from NAIA to Clark as no international passenger should have to experience security and transport nightmares just to transfer planes for his final destination in, say, palawan or virac.
i actually favor to just move everything out to Clark and sell the land where NAIA currently sits. im sure the land will command premium price as it is adjacent to makati, the fort, and old Manila/ Roxas boulevard. i'm wondering maybe the money raised from that sale would be enough to finance the central station and train link plus terminal upgrades of Clark? if not enough maybe it can form the government's equity in a JV with a private company, such as the current noisemakers in Clark, MVP. (assuming corruption is tamed of course...) or maybe the government can provide the transport link, then bid out the passenger and cargo terminals to a private company under the BOT for a 25 year lease. i think it's definitely feasible and we can have a new terminal in 5-7 yrs, a glowing milestone for the next CAAP head.
or of course we can also wait for one big plane crash in NAIA where hundreds of passengers plus informal settlers plus travellers in the SLEX go up in flames (god forbid!) before the government is pushed to do something about it.