Just off the top of my head, a second Tyrant is an auto.magic choice, and a second Veno, or Zoey looks like a good add on.
Automatically Appended Next Post: After that it depends on style, and the local meta. Personally I like having plenty of Troops, so I would add a Warrior Brood, with cannon, for some extra Synapse. It will also help you add a Formation. Adding a Formation to 1000 points will get you pretty close to 1500 on it's own.
Most anyone has good luck with adding Living Artillery Node.