I like this, looks very tropical and colorful. I like the terrain too. You won't get much out of the satellites for help on rivers so I suggest a few things:

1. Take a soft brush and paint in some river valleys/lowlands.
2. Put a layer of 50% gray between the land and river layers, set it to overlay, and use the burn tool to paint some valleys in.
3. Easiest but crappiest way is to add an outer glow of dark green.
4. Add some variation to the river line thickness by going back over places like bends and deltas (which I can see you already have some wider deltas).
5. You can always add a down-bevel to make it look lower, I've gotten mixed results.
6. Lastly, add a slight blur to soften the edges.

Anywho, looks real nice and nearly done, label this bad boy up.