Swashbucklers have 23 abilities, the least of all classes, and less than one-third of those need input from the character to fire.
Rogues have all but 6 of the swashbuckler's skills.
I think the best way to improve swashbuckler is to remove it.
Allow rogues to have all alignments, but lawful rogues lose the following:
steal/plant
disguise
backstab
dual backstab
circle stab
third attack
and gain:
dual wield
kick
taunt
finesse
enhanced parry
riposte
Or something along those lines. If rogues have d6 hit dice and swashbucklers have d8s or whatever, changing that might also be warranted as lawful rogues would essentially be front-line rogues. Unlawful rogues do things from behind. More or less.
Here's the "differences" version of the two classes, for anyone who wants to make their own admixture:
Code:
Swashbuckler:
Amateur
dual wield
Novice kick
Initiate
Apprentice
taunt
Journeyman finesse
Veteran enhanced parry
Expert
Mentor riposte
Rogue:
Amateur mace
whip
backstab
hide peek
Novice pick lock
steal
Initiate shield block
climb
Apprentice disguise
circle stab
Journeyman
plant
Veteran hamstring
third attack
Expert dual backstab scrolls