You're absolutely right that there is an insular mindset that emerged within the DC Beltway. And everyone else knows it - hence "not an insider" being an issue in elections. People have looked for ways around it - term limits, more time in the district, allowing more telepresence, etc. - but it's a tradeoff. It's harder to get things done in DC if you don't have that network of beltway relationships, and basic group dynamics says the insiders will close ranks against outsiders despite party affiliation. And that puts the parties' national committees in a complex position.
I won't go so far as to agree with your "farmable resources" statement, I think they just lose touch. The bureaucracy though... Yeah, while I'm sure there are some who don't care about politics, human nature tells me there are plenty who do, and more who are just interested in getting as close to power as they can. And then there are the people lauded as "institutionalists", who should instead be evicted. They're the ones who put preserving agencies/institutions above the missions of those agencies/institutions (that's what it means). I don't want an institutionalist running the CIA, I want someone who would be willing to tear its heart out and let it die if that's what the mission requires. J. Edgar Hoover was an institutionalist, and he was happy to use illegally obtained blackmail to preserve his agency. They may not be partisan, but they are petty tyrants.
But don't forget the legislative staff. Elected officials get changed out, they don't. And they're the ones who do most of the work, like reviewing and drafting legislation. So, there is an entrenched legislative bureaucracy as well. And the worst part is... what are you going to do? Fire the people who know how to get things done, thus shooting yourself in the foot? Because let me tell you, legislators don't know how to do anything. They won't even remember to staple their bills together before submitting them despite being reminded a dozen times and having their bills tossed in the trash (true story from Georgia's State House).
And as much as I prefer it when Washington does nothing, sometimes it needs to do things.
I may have rambled a bit here. I hope it wasn't too unpleasant.