My lust for new Sonar version is pushing me to upgrade, but my pocketbook is telling me no.  I already have Superior Drummer with several expansion packs and I have X2 Producer and am not too interested in Melodyne, since most of the vocals I record are mine and I can usually fix pitch problems by recording again.  What else makes this upgrade essential?
 
I do love the new comping feature so I'm thinking about just upgrading to X3 Essential.  Wonder if that would work OK?

You'd lose ProChannel. Maybe Studio?

Studio would also lose R-Mix and possibly other 3rd party plug-ins that were included with older versions of Producer.