Sounds like you have healthy robust hives, and may be well positioned for the flow when it arrives.
I am just a half zone north of you, and there is nothing for the bees to gather here just yet. I doubt the bees would build much comb with the up and down weather and just sugar to eat. Up here I would wait on adding another super. We are watching the maples closely here, they may bust out soon (earlier than normal). Once that happens, then the spring build up is on. Once you have a flow then adding a super may be a good move. Like BMAC said you may be in line for an early split, which would be sweet.