the easiest way to remember FF vs Crop is that you need to shoot with a higher focal length to achieve the same framing as a crop. You get MORE than a stop DOF control. Background blur (due to compression of higher focal lengths) will be more pleasing as well not to be confused with DOF. Thin DOF != background blur.
On top of buttery backgrounds, FF will give you sharper images with the same lens. If you look at photozone's mtf numbers, the nifty fifty + FF will BEAT a similar crop + 35mm F1.4 L..... let that sink in for a minute, then you realize how valuable a FF upgrade can be.
The old adage Glass over body doesnt apply in the digital age because you have really two different formats sharing similar lenses. FF vs Crop is like MF vs FF. It's a whole different league.
I'm probably rambling too much, but will leave you with this to see the differences in background blur with similar field of views: http://www.flickr.com/photos/8413...4096725884
FF also really shines in low light. I thought the T4i did well until I got a 6D. ISO 3200 is not a problem. Even ISO 6400 doesn't look bad.