I just tried that as well, and you're right, the results are similar, but I noticed some differences.
1. When you do the overlay effect some parts of the picture are more saturated (then my way) and some are less saturated, giving it a bit of an unbalanced look.
2. The image isn't as clear. (which could be achieved by adjusting the sharpness but then you're back to more steps again)
3.It still looks very 2-D with a kind of gray, filmy covering over it, not allowing the objects in the picture to present themselves individually.
Thanks for the idea though.
If you follow the link the picture on the left was done using the overlay mode, and the one on the right, using my method.
http://i1251.photobucket.com/albums/hh541/Hannah_Vlasblom/beforeandafter1.jpg
But even just doing the overlay does make a big difference, but doesn't give quite the same results.