In normal games I tend to take a coreplanet and set up shop there.
What it in effect means is that I can get a small, specialised, fleet in, nuke a target. Than get whatever is left, heavilly damaged, back on a planet of my own, repair and reinforce and relaunch the attack to take down the next target.
Doesnt matter much if you keep the planet on allert if you keep pummeling it. I however would not take a coreplanet if I am not certain I can keep the pressure up for say the next ½ to full hour.