When registering Melodyne for the first time, seems they offer an upgrade to "Editor" for $149 (or half price).  This version I notice doesn't offer multiple tracks at once, unlike their flagship version "Melodyne Studio Bundle" which in addition to Editor2 includes "Melodyne Studio 3".   
 
So... why would I want Studio 3 instead of just Editor2?   and....can you upgrade to that instead of Editor2, when given the opportunity?

Good questions. I'm all ears, as well.

You can upgrade to the Studio bundle but not at the super low special offered to Sonar users for the Essential to Editor version. It still costs $299 above that price for the Studio bundle.

With the Studio bundle you still. Get Editor and then you get a multi track Melodyne which is still 32 bit and vst2.4 unfortunately. While it does have a plugin it is primarily designed to work standalone. They are currently working on a 64 bit VST3 version.

Go to the Celemony site and check out the detailed comparison which tells you all this information and more.

Yeah...Ive absorbed all I could out of Celemony's site and the only thing I could detect was the studio bundle has the ability to do multiple tracks...and I'm not seeing how or why you'd use that.   I didn't see anything about the 32bit on their site either. 
However, the polyphonic upgrade for $149 seems pretty logical and I understand the uses there.  With the multiple tracks, I'm not envisioning the scenario.  Apparently you'd just pull up a bunch of them, like MIDI in the pno roll and just be able to change them, while still being able to reference other tracks.  Might be a deeper application of the plug that I'd actually use.  I like that their capstan plug is only $5000...or you can rent it!  That's a new one for me.

The one feature studio has that editor desperately lacks is generating pitch bend data In midi files when notes in the source audio files wavers. Very surprised that's not a par of editor.