If you are going to be playing the game for a full year, as a lvl 80, then why wouldn't you want to go sub? FTP should be for those who want to try out the game or dabble in the game but not pay to sub: if you want high end content or to do the bigger dungeons you are going to have to pay anyway.
15/month about pays for one night at the movies with a drink and maybe a candy bar, if you don't want 3D in my area. Probably not the candy bar or popcorn, though, come to think of it.