I am a big fan of painting in the shoreline. The views you get are just fantastic. Below in this blog post, there's a picture showing 3 steps in creating this painting.
SSU05 Seascape Plein air Painting "Girl in Shoreline"
Your Seascapes will get that spark of life in, when you can paint them there: standing on the beach.
Even if you don't live near a beach, you can book a holiday to a place near the ocean and start painting there.