I don't see a pun in the title.
funny you ask this as I have been walking around a lot with my 70-200 and not bothering to take any other lens with me and using my iphone as my wide angle camera. Seems to work for me, IQ is on par with just about any other mid range PS out there plus it has the advantage of being very light and something Id take with me anyway. It also is the best PS on the market for taking the photograph, doing some quick pp through snapseed and off to my facebook or flickr accounts. But if that doesn't work for you I'd invest in the 17-55 f2.8 IS over any of the wide to normal primes especially on APS C. Its way more flexible and you don't lose much if anything in the IQ department. My 17-55 was glued to my 7d.
I'd call that unacceptably soft. Given your shutter speeds, it's unlikely to be motion blur or camera shake (especially the second shot at 1/640 s). Could be the AF, could be the lens. I'd suggest testing with Live View and manual focus (or autofocus in Live View, as long as you're not using the quick mode where the mirror flips up) and see if that's sharp, as elflord suggests. If that works, you need AFMA on your 7D (XSi doesn't support it). If it's still just as soft, I'd contact Canon Service.
Looks like it could be out of focus. Did you try manually focusing in live view to determine whether it's the AF or the optics ? If it's a focus problem, you could try microfocus-adjusting (since your body supports it) and see if you can get the longer shots to work without messing up your macro shots.