I find it difficult to find paths up cliffs and such when attacking islands. The addition of roads to the islands (similar to those in stormworks) for the primary purpose of highlighting paths up cliffs would be an immense quality-of-life improvement.

Alternative suggestion: use a color-coding schema for altitude grading lines on the holomap and/or color land altitude in the "cartography" view of the vehicle control screen. Example: beige (low altitude) => dark green => light green => white (highest altitude).