My answer will not give you an advice like Buy or not this because as others comments it depends on many factors.
I can give my opinion about two things:
Nikon Full frame or stay to Canon:
I cannot say to change the brand except if you see a very needed feature that one brand have that is not equivalent in the other.
I am a Nikon lover and and I just want to give my opinion about the full frames of Nikon: they are not mature except if you take the D3 or D4 (even the D4 is a regression about the battery life).
If I compare with my old D300, all D700/ D800 or D600 are very expensive for what they give and they all have some design errors that I think unacceptable for that price range:
- D700 eyepiece does not cover 100%
- D800 /E max frames/sec at 4fps is quite slow
- D600 at 5.5 fps is still lower than the D300(s).
In my opinion the Full frame from Canon are superior in that (e.g. the 5D mark III).
For the cropped vs full-frame:
As other said "it depends" but I would say simply:
- If you mainly shoot nature photography (insects with macro lenses; birds, wild animals...) --> cropped is the best (because the crop factor)
- if you make landscape and like the extreme wide angle; like to push the ISO high because shooting in low light without flash --> Full Frame.
You have to know that switching to full frame will make you to invest more money than just the camera body: if you have many lenses for cropped bodies, you have to renew all your lenses. For all brands their full frame lenses are more expensive.
The advantage to stay with a Canon like 550D or 650D is that you can keep your lenses you used with the 1000D. In the other hand Canon have others more professional bodies like 60D and 7D which have the cropped sensors as well.
Now Nikon seems to found some improvement of the D800/E as they launch a D810 which does not have the bypass filter (equivalent to D800E) and with a improved maximum speed (5fps at 36Mpix) which seems to look like a perfect camera for architectural and able to do other things as well). That is erase all my negative comments Nikon full frame... the only negative point is the price but we cannot change that except waiting and waiting...