I've been taking everyone's comments and feedback to heart, and have made a few changes. First, I darkened the mountains as Steel General suggested, by playing with the lighting and contrast. After doing so, I noticed some issues with the terrain color layer that weren't as obvious with lighter mountains, so I touched up that layer with the smudge tool and a Gaussian blur. I also made the ice layer a little more transparent, in order for the peaks of snow-covered mountains to show through a little more clearly.
Next, I played around with various filters, trying to achieve a subtle foresty texture as Gidde suggested. I eventually went with two layers, one with a watercolor effect and the other with a sponge-painting effect. I think I like this, but I need to sleep on it and get a few opinions before I decide for sure about this style. Forests make up a huge portion of the western half of the continent, so I think it's important to get it right. I have noticed a few issues where the forest texture layer shows up in areas beyond the forest color...I'll have to clean that up if I decide to keep the texture.
I'm also thinking of adding a few more features...things like ruins, fortresses, wonders of the world...still thinking about how to do it. I don't want to clutter things too much. So that's something to look forward to. Any suggestions would be appreciated.