People spam her q because it's the most rewarding ability to use on a ** feel's good ** level. All her other abilities just kind of happen and aren't exactly noticeable, (Ult being the exception of course).
Heal's: Riot hates them. All heals are unworthy to exist alongside lifesteal, so it gained a shield, a weak one. And does anyone use the powerchord version? Regularly?
Speed up: Haha, sure, it's useful, it can save the day, it can win the day, but it just doesn't feel good to use. Not even the powerchord.
And so they Q. They always Q. It gives an aa buff to their ally, and hits two enemies and it gives visual feedback that you did something. Even the powerchord version is noticeable, since it's so simplistic.