I have had 2 BMX's that were cleared over bare steel......Both developed rust under the clear and were toast in short order. Clear powdercoat may last longer because it is tougher than auto clear but I still believe it's still asking for trouble in the long run because automotive clear coat and powdercoat do not chemically bond with steel. It only mechanicly binds by way of grabbing scratches in the surface of the steel. Auto clear is made to chemically bind with the base they are applied over........Not the best thing for bare steel.
I think it looks cool but I'd rather have protection.