Ghost ECL
I think that I would say about +6 or +7; it sort of depends on the character's class, I would think.
The character would lose Constitution, which for some characters would be terrible (how would a barbarian rage?). For spellcasters, however, it is not so bad, and the hit die increases to d12. Fly with perfect maneuverability is better than normal movement, but because of the speed 30, it is not so much better. Probably about +1.5 for these abilities.
The ability to be ethereal is good for escape, but not very useful in an adventure most of the time if the character wants to interact with enemies and such; travel capabilities are much stronger, and change the nature of the adventure setting drastically. Being incorporeal means that half of all weapon attacks will do no damage. Probably a +3.
The ghost is not a good attacker, but its spell-like abilities are quite strong (1d4 permanent str, dex, and con damage? Permanent Charisma damage with a gaze attack? Magic jar? Frightful moan?). All of these abilities are quite strong, usable often, and have reasonably high DC's. Add to this the fact that the ghost character is nearly impossible to destroy permanently, and you have about a +3 modifier here as well.
Now, without a ghost touch weapon (and even with) the character would do little melee damage, though he would hit fairly often. The reduction in armor class is a fairly major hit, also. This is where the class is important. If the character were a weapon combat character, like a barbarian, rogue, fighter, paladin, or ranger, the reduction in abilities here might reduce the ECL by a point or so. If the character is a spellcasting character, especially a sorcerer or bard, these hindrances will not matter very much, and the increase of d4 charisma permanently would make such characters very, very strong. For such characters, a -0.5 ECL, at best, or no reduction at all.
So, for a combat character, ECL +6; for a spellcasting character, especially a sorcerer, ECL +7 or +8.
I really like the idea, by the way. I have thought for a long time about how cool a ghost character would be.