I think that the wonder effects depend a great deal on level, as well. On lower levels, you have a lot more control over where they end up (because you will build most of them). Assuming you started up on a relatively large landmass, those wonders should provide the benefits needed without too much issue. After that, on lower levels you'll be rolling well enough to not need them much. It's just a matter of getting population in place.
Also at lower levels, by the time you are ready to really get rolling on a secondary island (even an unoccupied one), you probably have enough cash flow to rush granaries or whatever else you want, and absorb the cash impact. Not that you really need much in those outlying towns--maybe a granary (although if you are in worker add-in mode, you don't even really need that), a marketplace for sure (maintenance paid by Smith's), an aqueduct and hospital where applicable, and that's about it.
I'm only up to the early 1300s on my Regent game (on continents), and science isn't a big issue at all. In fact, I realized far too late that I have been pumping science far too hard in the early game. I'm researching Rocketry in 5 turns at 0% science on a Large map. In the early 1300s. I think I'll get quite a few future tech points just by accident. Had I put a lot more specialists to taxmen, I'd VERY comfortably been able to rush everything I needed as towns were created.