"Fishing boats are too expensive to build, way too expensive to buy, the tile yields aren't as good as in Civ 4 and the sailing tech path is an expensive early game detour that limits the effectiveness of pretty much every early game strategy (CB rush, NC rush, building the GL, rushing to your UU...)."
I agree that fishing boats for Fish resources is often uneconomical. I have plenty of games where even by the time I win, I have unimproved fish tiles in my core cities.
However, fishing boats for pearls, whales, and crabs are fantastic! The fishing boats work instantly (compared to the turns it takes to build improvements on land luxuries) and you can often chain them together. Rush buy a boat for 240, improve a lux, sell it for 240, to use to buy another boat to improve another lux. You'll be breaking even to set up all the fishing boats (which still net you extra tile yields) and then after those initial deals expire, you'll be raking in profit.
It gets even more ridiculously strong if you choose God of the Sea, because you can quickly generate an additional 2-4 hammers per turn by improving and selling all your sea luxes. That's a major hammer advantage at the beginning of the game.
It is generally agreed that the Colossus is a pretty terrible wonder.
Really? I think the Colossus is great! It's a base 5 gold, which is great in of itself. The extra gold for ocean tiles is nice if you are working resource tiles.
Furthermore, the only strategic resource available from ocean tiles comes very late in the game and is available earlier and cheaper on land. Since land-based Oil mostly shows up either in deserts (where Petra is strong) or marshes (where clearing them makes the tile self-sufficient in Food anyhow), coastal oil is rarely worth it.
Offshore platforms add a really nice production bonus, and IIRC, it stacks with Harbor and Seaport bonuses. As a result, an improved ocean oil tile can offer some pretty nice tile yields.
The Great Lighthouse is like God Mode on Archipelago, and if you play Elizabeth and go Commerce, it's basically unfair. But if there are no coastal cities to assault, there is virtually no benefit to building it, and if coastal cities continue to suffer these various disadvantages, no one will want to build them.
The Great Lighthouse is very situational. There are plenty of games where it is fairly useless.
However, one subtle but often valuable use is that on some Archipelago and Continent maps, the extra sight will allow you to make contact with major civs or city states that you otherwise would not be able to reach (due to ocean barriers).
Meanwhile, the Sydney Opera House comes very late in the game. If you are playing for a cultural victory, particularly on higher difficulties, you should desire a defensible location with a lot of production for wonders and defensive military units. Coastal cities typically do not meet this goal. If you find one with a long, snaky, single-tile connection to a larger water body with only one hex from which to attack your city, maybe consider it. But the map scripts I've seen don't produce such places often.
Sydney Opera House actually tends to be more useful for Science or Diplomacy games. If you're actively trying to win quickly, Cultural games are often over well before you reach Ecology. (You start the final sprint once you get Radar. You'll lucky if you can reach Plastics. But Ecology is still quite far away most of the time when I am ready for Utopia).
With sea and river tile gold going away, I'm beginning to wonder why anyone would bother settling on the coast at all. This goes counter to the almost universal human tendency to settle on the coast.
Access to additional trade routes.
Ability to build sea units. Having a landlocked empire really, really sucks!