Seaports - whats the point?

[mayormot 4]

[using $ for Simoleons here...]

A seaport costs $500/mo for 650 units of freight, and even when you bring funding down, it's still almost $1 per unit of freight shipped.

A rail station costs $10/mo for 2000 units of freight, plus maintenance on the rails, which is negligible to begin with - and the rails can also be used by passenger trains.

You'd need three seaports, at a monthly cost of $1500, to move 50 units less freight than the rails would for less than 1/5 the price. And for this, you *don't* get any mass-transit infrastructure as part of the package!
It occurs to me that since a seaport counts as the edge of the map as far as freight is concerned, freight would move slightly faster by seaport.

But is it really worth it? And if one uses one of the NAM's speed x10 plugins, the speed difference of a seaport vs. rail is practically nil.

So unless your city is an island with no land connections on any side, why bother building a seaport at all? If you do have land connections, is there something (e.g. demand cap relief) that only a seaport can provide, versus building more rail connections? Or is the seaport just expensive eye-candy for those who want to have one, just because?

[A Nonny Moose 8,261]

Basically, the seaport lets you have a freight sink without actually connecting to another city tile. It is also eye-candy, but I use it when I am doing a riparian city because it pleases me to do so.

The same does not apply to the ferries. They are very fast hydroplanes, and are usually better than a long bridge.

Edit: The simolean symbol,

[KoolSIM 2]

Besides, the Sea-Port also increases the demand-cap for Industry.