Using smaller clouds and with a narrower contrast between the extreme (lightest and darkest) shades to them might help somewhat. You could also add a wide band of shallow water around the coasts that gradually fades off, so that you won't have deep water areas touching the coastline at any point. Applying some texture to the water might also do wonders, but that really depends on if you can find a good texture to use.

Personally I'd be tempted to experiment with a nearly 'flat', very dark-colored ocean. I think something like that could work quite well with this coloring and those landmasses.
Click image for larger version. 

Name:	2dkivj9.png 
Views:	119 
Size:	807.6 KB 
ID:	46842

How does this look? I went more subtle with the clouds, darkened it, and added a band of lighter blended color around the coast that hopefully looks subtle and blended enough to avoid the floating cloud look. I think the floating effect is a lot more reduced now, though it might still be present.

I'm planning on improvising Ascension's Atlas style textures for mountains, forests, etc. Do you think, with the right coloring, this would be a good fit, or would you propose a different form of detailing?

I try to stay away from clouds layed down with a heavy hand. Use them very subtle and try to work out the sea with a brush. I tend to use a grunge brush with different shape dynamics. There is a tutorial by tear ( saderan if i remember correctly ) that helps you to create very beautiful oceans. But it takes some time and a tablet is useful ( that can be said in general , if you are into mapping and drawing get one, it´s a different world )
Oooo I might have to look into that. I'm not the most patient person in the world, but I'd definitely be willing to try it. I'll try the grunge brush technique if I can find some more information on how to make one and how to best apply it. I'll be hunting for that tut. If you find the link for it, please let me know. (Also, do you think that my revision helps)

Thanks!
Shadow