I disagree with the highlighted statement. I've spent many, many years in photography, both film and digital and though I agree that if someone is just going to use a camera for shooting photos of their tank, then the higher end full frame cameras would be a waste of money. With that being said, if one is wanting to pursue photography at an amateur level; landscapes, portraits, actions, macro, then it would be wise to purchase a high end camera now rather than later. I personally am waiting a couple years before I buy a new camera. Full frame allows one to have a larger aspect ratio and a more room to work with. I personally don't like my smaller sensor because I do a lot of macro photography and would prefer having my photos emulate 35mm size. The smaller sensors are much less than 35mm which is what I've been used to.
Edit: I do agree with everything you are saying Joe. Not trying to discount anything you've said. You can give two people unfamiliar with photography two different cameras, one an iphone, one a 5D. I guarantee the iphone person will be able to instantly take better photos than the person with the 5D assuming neither has photographic experience. Learning is the key with photography. Learning how to shoot only adjusting the aperature, then learn just using shutter speed. Once those two are mastered, you can start messing around with manual mode. I typically start with either adjusting the aperture, then the shutter speed, if I am unable to get the shot how I want it, I then switch to manual. Joe you've given some great advice. Number one thing that helps take better photos is learning the camera.