I usually reach for the Nord Lead 3 when I want big unison.
Can't see me using the MiniMonsta unison much since it maxes out my CPU (which is no slouch normally) at 1/4 of its unison potential!
The really useful feature of MiniMonsta over the real thing though (I have a Voyager for the 'real thing' ) is polyphony.
Minimonsta really falls down (along with other soft synths / VAs) when it comes to extreme resonance on (for example) self-oscillating filters. Unless someone specifically tries to model that kind of thing, I think we're going to get aliasing for some time to come.
That's where the real thing is still irreplaceable.