Sadly, I remember it too. The Haydonites' planet, Haydon IV, transforms into a giant, Unicron-sized mech, and destroys most of a fleet with its arm cannon. As I recall, it was destroyed by a Karbarran ship (the bear-people ) that flew inside its superstructure and rammed something critical, I guess.
As for this new trailer and RT: TSC, I'll probably watch it just for the nostalgia factor. Before becoming something of a Macross purist, Robotech was my big intro to anime (and to Macross). I don't have high hopes for it, though, although I'm curious to see how they resolve the SDF-3's dilemma by the end of it.