Weirdly enough, I agree with Elennsar about sneak attack not feeling quite right for the Swashbuckler. As much as I dislike Sudden Strike, I feel that it is a more appropriate representation of what the Swashbuckler is about. Then provide ways of making your opponent flat-footed verse you(Improved Feint/Swift Action Feint, acrobatic/cinematic charge). I also like the idea of an improved Persistent Attacker[CAdv] feat/class ability. This would allow a Swashbuckler to thematically keep an opponent off guard (sacrifice sa/ss for opponent being flatfooted next round) once he has found/made an opening in their defenses, constantly forcing them into a state of less than optimal defense.
Besides what I am pondering for my own campaign, I vote for point 2. At higher levels characters really need abilities that are 'big' and 'meaty', such that the abilities have a certain weight to them when said/thought about. I think this is one of the bigger failures of the PHB classes, that they drift off into nothingness (Fighter, Monk, Ranger, Paladin especially). Basically, the Swashbuckler needs some higher (14~20) level abilities that say "Look at ME! I'm a Swashbuckler and I'm AWESOME." The ability doesn't necessary have to say that ingame, but the player should certainly be thinking that right before he activates/uses it. If not, he might as well multiclass/PrC out to get an ability he does want.