i don't know civil 3d well, but we do use an fxl for field work and use the coding to autodraw a full civil 3d drawing. these were provided by our client, so i can't answer your specific question. but i would assume you are headed down the right path and the csv or space delimited file should be able to load into civil, or it might have to be manually done.
i just have a couple comments:
any symbols from the fxl will not follow in the csv.
civil has it's own line control system associated with certain codes. so you either have to change your fxl to match the civil default codes(this is the approach we took so that anyone that imports the points does not have to change the line control settings in civil) or you have to change the settings in civil to match your fxl. also note: i am almost positive that line control codes like connect point in fxl would be CPN 156 but in civil it would be CPN156. there is a space in fxl but no space in civil. another example for close line: fxl uses CLS 233 and civil would be CLS233. i am not aware of any way to fix this. if others have a solution please let us know.