For my band, we double tracked the vox and to me that was the thing that made them sound so good and stand out in the mix. Our vocalist did them pretty tight, and he would change his voice slightly for each track, so summed it was huge. We experimented with a little bit of panning and it was cool, but didn't fit the vibe of the songs or EP, so we cut those. But, if you were to pan, my vote would be subtle panning and not hard panning. You get a nice effect panning them hard left and right, but the stereo spread leaves the middle empty and makes the vocals feel a little wimpy, IMHO. Even with 10% panning on each side with 2 vocals takes opens the space quite a bit. Also, we didn't add reverb or anything to the vocals tracks, just a lot of compression (we added a touch of plate reverb on the master buss, though). For backups here and there, we added additional overdrive to the vocal tracks. I wouldn't use distortion for the main vocals tracks myself, but if you do, a LITTLE goes a LOOONG way, IMO. I'm no pro, but these are what I found to be when I recorded my bands album.