However, yes, I too would balk at the offer to give them more money for "faster" internet when they cannot deliver the current "slower" internet you're already paying for. It is pretty ballsy for the CS to even ask, but I suppose they are required to.
I think you're pretty quick to dismiss the local DSL provider. How bad can they really be? Keep in mind that review sites only list negative experiences, and I bet you can find just as many Comcast negative reviews as them.