I play on small map sizes as otherwise you get so many cities city management becomes a real pain and you have to wait ages between turns. I quite agree that if you are stuck on a small island the lighthouse would be of much greater importance. But I still think it's better to save your 200 shields for Magellan which lasts forever. But you can still concentrate on totally populating that island and building bigger cities with more improvements. Also a useful trick is to send your triremes two squares out and back again thus checking more ocean and usually spotting land - eventually. Seafaring halves the chance of being lost at sea, and Navigation isn't that difficult to research. The only real use I find for triremes is to map coastlines early in the game, explore goodie huts and establish contact and embassies. Forget trade or war as they are slow, can sink easily, can't fight and only carry two units. Diplomats can be used to close the science gap later. Also if another power puts a colony on your island, you can gain two advances by stealing from and subverting that city. You only seem to be able to demand tribute from a power if it has some cities on your continent. Also it's more fun if the other civs actually have a science and production edge as it makes the game more challenging.
"To me, the next most important Wonder, after the Pyramids, is the Great Library... my logic is I can put my taxes at 70% to build up my "bank account" for any emergency... i.e., rush jobs, war, etc... With the library, it means I don't necessarily fall behind on the techno advances, siphoning off the work of other Civs (I always play max civs)."
But you might miss the crucial advances that allow you to build new wonders thus giving your enemies a head start.
"I also place a higher premium on Leonardo's Workshop as I always keep a large military at the ready for defence and expansion and utilise a large number of settlers to improve my production, especially since I prefer to run a communist government as it allows me greater dictatorial control... Having to upgrade my military especially, proves to be cumbersome, even at "selling off" archaic units..."
I think it makes the game too easy.
"I also put a high emphasis on Statue of Liberty, so I can get to Communism, usually by the 14th century or so as it eliminates corruption and makes my military more effective..."
That's a good strategy.