Will entirely depend on your demographics. At $12 to $15 per person, that would be a non starter around here. Even with what you are describing, which would sound worth it if you always kept high quality.
From what i see, even people with money, they only want to spend about $8 to $9 per person per meal (and i still see people complain about that). Quality no longer seems to be a concern with the majority of people. It is all about cost.
If you did do all you can eat, i would suggest doing it Olive Garden style. First platter is large and has everything a normal meal would be. But each plate after that should only be 25% of the first, and it would require either a server to deliver it or, have the customer go up and get a refill somehow. This process will reduce waste from people taking/ordering more then they can eat and you losing money.
