I think they'll use their new engine cover seen in testing, Melbourne weather is not so hard on engine so it's predictable.
Talking about last year developments i think they had a bigger margin to develop, they fitted an "hybrid" DDD and developed the best F1 KERS system, that made huge difference, this year I dont't expect them to do the same "big step", not to mention Ferrari is completely focused on this years championship, Brawn is in theory stronger in development because of mercedes backup and RedBull is that fast and fragile team that just needs to be regular.