My option would definately be #2. I use FP in the Realms and have invested a lot of money in D&D stuff - and I wouldn't be too pleased if I couldn't those books with Freeport any more.
5. A sourcebook with information on running Freeport in different periods in its history (Great Raid/founding days; Milton Drac's reign; the new succession crisis; etc.--perhaps even a very brief section on Valossa's heyday).
Now this is just what I was about to suggest. I repeatedly thought about running a Freeport campaign in the Golden Age Of Piracy before the rise of the first Drac, so a sourcebook or a chapter on running Freeport campaigns in other eras would be very nice indeed.
Naval combat rules would be a give-away in my opinion. Not entirely necessary but still quite nice. I use the rules from Corsair, a PDF from Adamant Entertainment (the guys that wrote Skull & Bones). Basically it's the same system as presented in S&B, but it is independent from the Skull and Bones Setting and fits perfectly into standard D&D - and it brings the Legendary Vessel, one of the coolest inventions I ever came to stumble across.
As I use FP as a plugin-setting I'd see no use in an expansion of the world for my campaign. A short chapter could be easily ignored of course
Update the rules to 3.5, advance the timeline, publish the book as a 320-page full-color hardback and I will be the happiest buccaneer on this side of Hell's Triangle