Have a Nikon D7000, think I want a Canon 5d (original) instead?

I currently own a D7k w/ about 15k shutter clicks and have owned 6 other Nikons. I really enjoy my D7k, it has had no issues but I often want wider shots. I don't often take pictures past 100mm on a cropped sensor so I'm thinking full-frame might be for me. The only Canon I've owned was a 40d and didn't care for it. Two questions: Does a full-frame sensor really allow more light which would have me using lower ISO settings and thus better image quality? Also, does anyone think the original 5d is dated technology? I was Really impressed by the colors that came through on the 5d even though it's 6-7 years old. Plus, you can pick one up for $700-$800, and I think that's a steal.

"Does a full-frame sensor really allow more light which would have me using lower ISO settings and thus better image quality?"

No, the ISO is measured in the same way as before. A full frame sensor on the other hand performs better in high ISO situations.

"I often want wider shots"

Keep in mind that lenses that cover a full frame usually have e.g. 14mm as well. You can't use a 10-20mm crop frame lens on full frame without vignetting.
14mm is not really that much wider than the best ultra wide angle lenses for crop frame sensors.

How wide do you want?

No, a full frame sensor will not let in more light to allow you to have lower ISOs. Only the aperture of your lenses will allow you to let in more light to have lower ISOs, full frame sensors generally perform better at higher ISOs - they show less noise. But with a camera like the 5D Mark I, it's very old so it's ISO performance will be nowhere near as good as your D7000's. The 5D Mark I is quite worse when compared to your D7000 in all fields. The only thing it has going for it is that it's full frame.

I would recommend that you not hop between camera manufacturers so much and invest in one, buy good quality lenses with fast apertures and upgrade your camera body with that manufacturer. It will serve you better in the long run. At this stage I would say, stick with Nikon. You can buy a full frame Nikon camera for the same price as most Canon full frame cameras. Look into the Nikon D700, it's a full frame camera. But to be honest, your D7000 is a fantastic camera. Just buy a wide angled lens and you'll be sorted.

If you've already owned 6 Nikons you probably have some lenses for them, too. Ditching everything right now for an old 5D doesn't seem like a good idea. Yes it is full frame but the D7000 is still the better camera.

No, the full frame sensor is just better at high ISOs. If you needed ISO 1600 in a certain situation with your cropped sensor, you will need 1600 with a full frame camera as well. The full frame sensor will handle the noise better, though (assuming both cameras have roughly the same "age").

Get a wide angle lens for wider shots. A Sigma 17-50mm f/2.8 is a good choice. If you wanna go wider, you can look into a Tokina 11-16mm f/2.8 for Nikon. It's a great wide angle lens. 11mm on your D7000 would be the equivalent field of view of roughly 16mm on a full frame camera. That should be wide enough. If you really need more than that, then grab a like a 8mm fisheye lens.

Going from Nikon to Canon is a terrible idea and and going from a new body to an older body is a terrible idea. You're impressed by the colors produced by the 5D? All DSLR's images can be processed to give identical color. Get a Tokina 11-16 and that'll solve your problems.

Keep your D7000 and get a wider angle lens. A large image sensor won't let you choose a lower ISO, it usually has less noise at a given ISO compared to a crop sensor IF you are comparing sensors of the same generation.

The high ISO performance of the 5D compared to 2010-2012 dSLRs is poor. To get more light to the sensor to keep ISO down, it's all about the glass, so that's aperture and actual t-stop or light transmitted. Color, that's more about shooting RAW and your post processing software and skill. Also the auto focus system in the 5D and 5D MkII weren't great, that's no secret.

The original 5D is very dated, not worth it unless it's an absolute steal. Better to find a Nikon D700 (full frame) that's used, I've seen them all over the place price-wise from 1300 to 1900 US dollars. That image sensor was used in the D3, and it smokes not only the 5D, but edges out the 5D MkII as well.

The Sony sweet 16 image sensor is found in your Nikon D7000, Pentax K-5 and Sony A580 is amazing. These three dSLRs are also the highest rated sensors ever for crop sensor dSLRs according to DxOmark.