Is airpower useful in WinSPMBT?

[PlasmaKrab]

First question: how do you plan your strikes?

Better choose an entry path with good visibility, no friendly units along the way, no obstacles... so your aircrafts will have no parasitic signals and spot the targets without worries.
Pilot experience plays a big part though.

Admittedly cluster weapons often seem to be quite useless, though you can have some really good (or tough) surprises, and you cannot turn them into miracle weapons either.

Guided weapons work well against armor, but tend to eat up much loadout and strike time. In your game context you should find some good F15E with GBUs all over.
Against infantry, napalm/FAE is a must.