How can one make melodies made from whole tone scales sound more interesting & appealing? Unlike melodies based in a certain mode or a key, whole tone scales use only tones as the intervals. This is something which our ears are not normally attuned to. How do I write whole tone melodies more better?
This is more of an extended comment as opposed to an answer.
Whole tone scales are difficult because they do seem to wear out their uniqueness quickly, for whatever reason (I'm not so sure why).
General tip for learning composition: find works that make use of the material you want to know better and internalize them, analyze them, and try to understand them from your own point of view. Take a look at these two pieces:
Both of these composers are, of course, absolute giants, but you'll notice that nobody really can just stay in a single whole-tone scale, and have to juxtapose it against other sounds or other whole tone scales. I'm not so sure why this is (perhaps it's too symmetrical to create sufficient variation?), so it is often juxtaposed against other scales or melodic/harmonic material. See the following for a very good example of this:
The A section of this tune is heavily whole-tone, juxtaposed against other harmonies in the B section for contrast (and release). All this being said, you might have to add contrast to make your whole tone melodies more salient and listenable.
As the given examples show the whole tone scale can't be made much more interesting. The exciting element is the rhythm!
I don't know why Bartok and Debussy are stuck to the scale lines, could be in respect to the performers who maybe beginners). I also used whole tone lines in a V7b5 chord and only once in a quartet as in parallels of thirds. If I knew a better answer I wouldn't tell it as I would like to keep this secret like a cooking recept for myself.