Firebird the 64bit Melodyne VST is installed in a weird location initially. Look for Melodyne.dll and move it to your "common" vst folder and rescan. It took me awhile to figure that one out.
I've never used AutoTune but Melodyne is killer at tuning, IMHO. I one recorded a bass track where my bass was slightly out of tune. Ya, I could have re-tuned and re-recorded but for fun I ran it through Melodyne. Done and done.
Fair warning; if you need to do a lot of edits in one take, use the single track (i.e. standalone) version. There is still a problem in 64bit occasionally crashing when you do too many edits. Alternativey, edit and bounce to clip frequently.