The most popular splits for MCed Swashbuckler these days are bard 15 / ftr 3 / rog 2 and bard 12 / ftr 6 / rog 2. Both get you at least 2 extra feats and access to Stalwart D. defensive stance; 13 APs gets you +25 PRR/MRR and +20% HPs which is a big boost to survivability. The bard 15 builds get to keep lvl 5 spells and
Inspire Excellence; while the bard 12 / ftr 6 split can take advantage of Swashbuckling and Strike w/No Thought stacking using handaxes or light picks. So: better party buffs or better personal DPS, basically.
However, since you're already bard 16 / rog 2, your options are more limited (unless you LR). If you did splash two ftr lvls, that would let you take both Shield Masteries; then you could either keep Toughness + Extend or swap them for something else if you wanted. Skills pts could be an issue though.