One thing is for sure, many teams will have a couple of small tweaks, but nothing spectacular like a new wing or such.
Id say either Malaysia or most likley Barcelona will be more probable. Take Lotus as the prime example, they have new suspension parts and a couple of other things coming for Malaysia, and they have a new gearbox coming for Barcelona.
This should see a 75% improvement in lap time, whitch is about 3 seconds.
If Force india were to come up wit a new front wing worth 0.5 of a second, thats roughly about a 20% improvement in lap time roughly. Highly cynical that a front wing can improve that much. Im tryacking the improvement in each car this year, race by race. So far Best is Ferarri, worst is Hispania. The hierarchy is this so far:
Ferarri, Red Bull, McLaren, Mercedes, Williams, Force india, Renault, Sauber, STR, Lotus, Virgin and Hispania at the rear. Thats all on % gain to P1 in Quali laps.
Im happy to eat humble pie if necacarry.