...may well be something that gives you better IQ and was cherished by an amateur rather than abused by a pro.
Most times, I'd rather have something abused by a pro than cherished by an amateur. A true pro will get their gear routinely checked and maintained meticulously (CLA at least 1-2 times yearly). The slightest bit of oddness from a lens or body would usually get sent and fixed promptly. The amateur would usually not notice the variation or find it acceptable. And, if you've ever (really) dealt with estates, the amount of gear that's sitting around and rotting or found in a closet fungi-fied or with dried seals is mind-boggling.
I've almost always preferred used gear over new - get better equipment for less money. The key to is to getting it from a real used dealer with warranty. I tend to use the hell out of gear. Most of mine look like somebody's dragged it through mud and across a parking lot, paint missing off bodies, lenses with not a single screened character on the barrel visible. But, at least twice yearly, it all goes to Canon for check and clean. As soon as a piece sounds, feels, or seem out of spec, it gets sent to get repaired. Even the backup gear gets checked and rotated into service. And, there's pretty much backups for everything!
With that said, the hardest thing (and costly) is to change systems. If the OP's been a Nikon shooter, their best bet would be to stick to Nikon and invest in a newer body or something used like the D700. Yet, since they don't have much Nikon gear, they could always save up some and switch it all out for something like 5D2.
I don't personally care for video from SLRs - if I wanted motion, I'd go shoot an Arri (talk about a costly switch!).
As for the color, there is a subtle difference between the outputs from Canon vs Nikon/Sony sensors. The Nikon's I've shot seem to have a more "pastel" like pallette, no matter how much post processing I do. The richest output has been from Canon and Leica.
Full frame is nice for wide work, boken, and crispness of an image (larger sensor=more surface area for equiv mp output). However, APS-C and APS-H can make the tele end nicer if needing the reach. There's always saving up a bit more money and going 5D2 w/ 50/1.8...