I think without the 'disparity', the power in each state swings so far to the most populous areas, aka the cities, which will basically negate any power non-urban areas would have. Further down the road, I believe making a CITY a state sets a bad precedent, because then Los Angeles, Chicago, New York City, etc. will want to follow suit, and this will be the justification.
Not that I'm unique here, but as someone who grew up in one of the counties in MD that borders DC, I know that DC residents use the addresses of friends/family that live in MD (and probably VA) to enable their kids to go to schools outside of DC. I'm not judging here, only pointing out that this practice (it's doubtful any concrete numbers can ever be produced that would show how prevalent it is), and probably other similar practices to take advantage of the benefits provided by neighboring states are causing a drain on the bordering counties and states economies. To me, making DC a state probably wouldn't change this issue, as I doubt the DC school systems and local programs (welfare, social services, etc) will magically change into something more desirable, so from a more politically neutral perspective, I think while it would be complicated, making DC residents fall under MD and VA for voting and administrative purposes makes more sense. On the MD side, the two counties that would be most affected, Prince George's (the richest per capita African-American county in the country) and Montgomery (one of the overall richest counties in the country) pretty much dictate the politics for the entire state already, so this wouldn't really tip state politics much either, and the DC citizens would get their beloved representation.