Upload & Sell: On
Moving up from a Rebel XT/350D to a 5D really made a difference to my photography. Better VF, image quality, handling. And a real improvement in the pictures i take. The problem is that the big improvement was in my portraiture and use of shallow DOF. For wide angle landscapes, i think i still prefer the crop/10-22mm combo over the 5D/17-40mm. If i printed big i'm sure that would change, but i don't.
Right, bigger sensor and it's easier to get shallow DOF... not the other way around. (which is fun to have the ability to grab, just not my primary concern)
Which makes the ts-e lenses even more interesting.
As you alluded to, though... crop sensor, in good lighting, will pretty much do just as well as the full frame. At least in canon's lineup.
Of course the low light performance I'm after is one of the big advantages of a bigger sensor. . .