I'm looking for a (Logic) plugin that duplicates a track a couple of times with the option of a slight offset/detune for phattening the sound of a software instrument or sample-instrument. Any suggestions? Anyone?

 

I'm unaware of a plugin to do that specifically, but I would:

1) Press and hold Option key when dragging the track to duplicate it and all of its audio/MIDI.
2) Add zplane Elastique Pitch AU plugin to the duplicated tracks. You can type in a 0.01 semitone value if you want.
-Or, there's the more basic one included with Logic

Or use two sends on the original track and put one of the plugins I mentioned on each of them, tuned slightly apart.

 

How about adding a slight Harmonizer to your second track? Maybe? Good luck.

 

Chorus.

 

'ADT', 'artificial double tracking'. Running a second track through a (2nd) tape machine.
In plugin world, the plugins add a bit of wow & flutter (almost unhearable, but enough to add some randomness to make it different from the original) and delay. Pan the source left, pan the artificial-doubled track right, tadaah.
Waves has an ADT plugin, and there is a free one from vacuumsound (that appears to have an AU plugin for mac, 'universal binary', does that work on Logic? I have no clue on the mac plugin-world) at http://www.vacuumsound.de/plugins.html.

Playing with Acon Digital Multiply (free, winner of the last KVR plugin-code challenge, and there is an extended paid version now) is also recommended to try to fatten things up.

 

In Logic, duplicate track with original audio
Add Logic sample delay

 

What do you get out of duplicating the track, in relation to say a send/aux to one or several modulation effects (in serial and/or parallel)?

 

OP just wanted to duplicate a track and offset it, so that was the simple version

 

Found this: Loomer Manifold. Duplicates, pans and detunes the track's audio output in real time up to 20 fold!