I agree with the others about outlining the horses/grass/trees.
For the rest of it, I certainly agree that SITD could look nice. Personally, I usually try to add in some design that ties in with either the fabric or the piecing. An all-over horse shoe filler might look nice. Or you could SITD the colored pieces & do a horseshoe filler in the cream parts. It would add some curves to your quilt, helping to balance the design.