I have both. In fact, I started with Essential about a year ago and upgraded to Editor just recently. I like them both for different reasons, and I probably use V-Vocal the most. Often, when pitch correcting, I'm just a hair off here and there, so VV is quicker and sounds just as good, to my ears. It's been integrated in Sonar since version 5, and I've never had problems with it as long as I work on short segments and bounce to clips when I'm done.
Melodyne is very handy for stretching and moving notes, and if your more than a hair off pitch then it may be the better way to go. I still bounce to clips afterwards, though I've had several instances of Melodyne going at once. Essential basically can do what VV can do as far as pitch and timing goes, but it lacks the formant control of VV and the ability to control the vibrato of a note.
To sum it up, they're both very sophisticated programs that can perform small miracles. $50 is an affordable way to get into the Melodyne family, and I got a special deal to upgrade to Editor for a very good price, so you may, too. I've only needed to use the DNA technology of Editor twice, but I'm glad it was there when I needed it. Most people here will probably tell you that Melodyne is the way to go, but you won't be crippled if you don't buy it.
Best of luck!