I'm not sure I'll ever be able to build a Munitions Booster again - I feel like I've betrayed them.
Their main use, in my experience, is boosting squadrons of bombers that are attacking hardened targets, such as forcefields. They're also somewhat useful for wormhole defense.
They are destroyed fairly easily though, so I often feel that their caps are quite low. Perhaps if they only worked while static, but boosted ships within a larger radius? This might make it easier to keep them out of harm's way. For example, while attacking forcefields, I could park them behind the bombers, hopefully keeping them out of the range of the turrets that would otherwise destroy them.