Widescreen monitors just distribute the square inches in a different way, there's not any less than a non-widescreen monitor. And even if your video card doesn't support widescreen resolutions, which I doubt you'd find a single example of still in use, the monitor could perform the necessary scaling of the image to make it fit. It won't be as good if it's having to stretch a non-widescreen resolution, but it will get you by.
You are correct on the power consumption however. One of the most power hungry LCDs I know of, is the Dell 2001FP (20.1"), and it only uses a maximum of 90W. That's with the sound bar attachment, and maxing out the built-in USB hub. For some perspective, that's about the power draw of your average 17" CRT.
The other nice thing about LCDs is the space savings. You don't need all that extra housing for the guns, so the entire thing is only about an inch thick. Most of them are designed to be wall mountable. Less power draw means less heat being pumped out as well. Maybe not so nice for people in arctic regions, but for those in more humid climates, it can be a real boon.