I understand that one reason to use multi spark on a carbed engine is to ignite the unburned fuel on the low rpm side. Would the same train of thought be used for an efi engine? Or would there be no gain?
The biggest reason for the multisparks is that they're usually (not always) paired with CDI ignitions. An inductive ignition (like the Mopar electronic one) gives a good long spark at low RPM. A CDI ignition can't do this and fires several sparks to compensate. But at high RPM, the inductive ignition can run out of time to charge the coil, while a CDI ignition still keeps firing on full power. Multispark and CDI boxes have about the same advantage on EFI engines that they do with carbs - they can deliver more power to deal with higher RPM or extra cylinder pressure.
Newer ignition systems get around the charging limits on inductive ignitions by using more coils and ditching the distributor. Some of them even multi-spark with an inductive engine, something that would be tricky with a distributor.