If you cant get a good picture out of a 1000d body, then upgrading isnt going to change that.
Upgrading your lenses "could" improve your outcome, but that will depend on what your "problem" is.
The image sensor is probably the same as that in a 40D, the electronics driving the chip would have some improvements, but the sensor would be the same.
5D etc are a larger sensor, but is sensor size your problem?
What are you trying to fix?
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