Hello, can you be more specific about your IQ problem ? You speak about not being happy with your camera and want to change the lens. These are 2 different problems. I can't talk about the 7D since I don't have one, but I can give you my opinion about the lens.
I am not sure you would improve so much the image quality with the Tamron, you can go here : http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=242&Camera=453&Sample=0&FLI=0&API=0&LensComp=470&CameraComp=0&FLIComp=0&APIComp=0
to get an idea about IQ of the 2 lenses compared. Some focals seem to be a bit better with the Tamron, some better with the Canon. The main advantage of the Tamron is it's closer focusing distance, that gives it more possibilities, BUT you would loose the USM AF and the quality construction of the Canon L.
Honestly, I think the Canon 70-200mm L 2.8 is not the issue here. Yes they are newer and slightly sharper lenses nowadays on the market, but unless you would want to upgrade for 70-200mm 2.8 II, (which I agree Canon has once again a bit overpriced), I think you will regret the field qualities of the Canon.
Thousands of pro photographers have found the Canon 70-200 f2.8 being a good enough lens for almost everything, IMO the switch to Tamron won't change much to you IQ. Maybe you got a bad one, but on my own I have the IS version of yours, and I don't think the V2 of this lens would change my IQ in such proportions it's worth the money. To be honest I never thought about replacing it, as it still does the job more than I would have expected.
This being said more information about your IQ problem would help to give more specific answers.