I had to catch the bus home when I wrote my previous post, so here's the more extensive version:
Not just the towns, but the islands as well, should all look unique. Each town should be different from the others and you should be able to see their nationality based on the architecture.
The islands should also look different. In PotC and other Storm-engine based games, all islands are basically green cliffs with some towns on them.
In the real Caribbean, islands are a lot lower, with sandy beaches and such. So a mix between cliffy islands, sandy islands and rocky islands would be a lot more interesting.
The towns and jungles should also properly be modeled onto the islands so you can see them from sea and the directions are correct (eg. NOT like OUR new islands! <img src="style_emoticons/<#EMO_DIR#>/24.gif" style="vertical-align:middle" emoid="
" border="0" alt="24.gif" /> )
Each island might even be partly rocky, partly "cliffy" and have a sandy beach or two as well. As long as there's something "special" about the islands.
If possible, it would be especially nice if the islands and the towns would, at least somewhat, resemble their real-life historical counterparts.
If this is too much work, personally I would rather have less islands than everything looking the same.
After all, I do not believe there's much gameplay value to be gained in having "a lot" of anything.
Dozens of ships, dozens of weapons and dozens of locations is not going to make for an interesting game, unless a lot of things are done with them as well.
This is still apparent in the "New Horizons" mod; we've added a lot of new islands, but even three years later, the "filling up and making use of the locations" process still hasn't been finished.
Of course the town design is part of a more extensive nation- and period-specific "variety" feature.
Other things that should be subject to this are the character models, ships and weapons.
The characters of a certain nation should be recognisable as such, as should be the ships and even the weapons could be nation-specific.
In addition to the graphical differences between nations, there should also be gameplay differences.
Each nation should have its own strengths and weaknesses and offer different advantages and disadvantages to the player.