The reason I ask is that I've started a game on a small island (barely room for three cities packed in as tight as possible, but with a trio of tiny islands for company), and a resourceless one tile island is the only place left to expand into before Astronomy.
Being financial, and with the colossus already built in my capital, coastal tiles bring in 4 commerce each. And it's a standard size map (and I'm only playing noble/vanilla), so the maintenance costs are tolerable. It's early days, so there's time to grow the population (once the lighthouse has been built) for future whipping/drafting.
The question, I suppose, is whether I should bother with any more buildings after the lighthouse... Or if, on the other hand, I should just save myself the settler build and concentrate on military units instead...
(Incidently, this start is a little out of the ordinary because I've got 18 civs on a standard fractal map, and I used the worldbuilder and repeated map regens to find a financial AI civ starting on a tiny isolated island, and then restarted from the worldbuilder save. Thus far I'm racing ahead in tech; with all that sea and no need to build a strong military I expected as much. The problem is that several mainland civs have started to conquer their neighbours, I can't get in on the action until I get Astronomy (which will knacker my colossus-reliant economy), and my production will never keep up with the mainlanders once they get developed. So I'm looking to squeeze every last beaker/gold/pop/hammer out of my empire to pick up every possible military advantage before the AI gets Astronomy. Then I'll trade for it, use my gold reserves to upgrade my forces, whip out an armada, and go a huntin'.

)
ps. You can get two hammers from the city if you use a citizen specialist!
Edit: You can get three hammers from the city if you run mercantilism and use two citizen specialists!!
