Any chance you can post some better pics? The first things that popped out at me were taking down the window treatment and everything from the tops of the cabinets. I would also consider adding a runner to the floor to lighten it up - you could get something indoor outdoor so it will survive the kitchen.

You would be amazed at how much "lighter" it will seem if you can eliminate "stuff". Can you begin by clearing away everything up in the soffit area and add soft lighting up there? Right now the objects are weighing things down and casting shadows. Then work on the clutter on the countertops. Also, do you really need the valance? Just removing that will add more light. Finally, can you paint just the island to a lighter color?

It's true that de-cluttering can work wonders. I wonder if you could paint the perimeter cabinets a lighter color, but keep the island in the dark wood tones for contrast.

I'd change the valance to a bright, pretty color, get some runners to coordinate, and dress up the cabinets with some shiny hardware. If that doesn't do enough for you, I'd consider putting in a new, light colored backsplash. I can't really tell what backsplash you have now. Can we get a close up?