Widening a track

The delay version is going to be slightly heavier on the CPU but only by a tiny amount, definitely not worth worrying about. A basic delay is very CPU light.

Because the delay is software based it would use more CPU, the track method uses more disk I/O but nether should be significant enough to matter unless multiplied many times over.

If you have time play around with the Haas effect. Make a copy of the track and slide it by ~ .3ms to .7ms. panning the channels all the way left and right. It will place the instrument in a different space in the stereo field. Haas Effect

You more or less described it in your OP. It's just a copy of the same signal with one slightly delayed. There is more science to it than that but AFAIK that's the basic principle. They used to use it over public amplification systems so things were more audible... due to the perceived "width" of the sound.
 
I have been told multiple times though that a stereo delay plugin will achieve the same thing... which you also described in your OP.

lol... near simulpost.

You can also use Channel Tools to do this. Just add it to the track and enable the delay you want for each channel.
 
Regards,
Dan

If you play tracks 40ms apart back in mono, you'll encounter a slapback/flamming effect. This isn't always a problem, of course, but something to think about if there's a chance of mono playback (e.g., TV).
 
Also if the purpose of widening is to create a sense of space, I do that all the time with the Sonitus Delay for guitar amp sims. I feel much of what makes an amp sound like an amp is putting it in a room, so the Sonitus creates short "reflections."
 
I'll set the delays to two short prime numbers, like 23 and 29 for a bigger space or 17 and 19 for a smaller one. The reason for prime numbers is you can add a teeny bit of feedback and there won't be a resonance build-up in common with the two.
 
Then link the two Delay Mix controls for the left and right channels. At 0 you have no "room," at 100 you have super-wide stereo which sounds unrealistic to me. I usually set the amount of mix for around 30-40%. It gives a realistic sense of room space.