I only noticed the tree/grass was digital in the high rez version. Did you make 3D renders in both pieces yourself?

For Red Dimension, I'd recommend you try to keep a visual theme for the vectors. The flowers/blades have an emboss/3d effect to them, while the hearts don't. Gives me the impression that they don't mix in.

Some quick technical advice: if you want to avoid the stepping stone gradient (from gray to white) effect you see in Red Dimension, create higher bit files to work with. If you use 16bit instead of 8bit the effect will be less pronounced (or not visible).