Why does Portland care if these MAGA people are the drain on resources they like to claim?

Yeah Congress would have their own opinions based on precisely how this impacts Fed politics, which I don't know. I suppose if Idaho is conservative and Idaho gets bigger and thus more influential, then the impact is pro-conservative. A conservative Congress might then approve it. Similarly, if it ends up shifting a seat or something in the direction of the Democrats, maybe they could be talked into it.

At the Federal level probably not, because this sounds to me like DC becoming a state. It has political effects, primarily pro-Democrat. DC never becomes a state.