Actually now that I think about it, Congress barely passes any bills anyway anymore so that would be tricky for them, but since many of them are there for decades, they have plenty of time.
Term limits really would make sense.
Term limits empower the influential actors that aren't directly accountable (lobbyists, professional staff, etc.) because the people that are directly accountable don't have the experience (unless gained through those other avenues) to be effective, and don't have a future in the institution (except as influencers in those other avenues). They don't actually address the problems you point too.
Lots of state governments have legislative term limits, and many times have much more of the same kind of problem you seem concerned about.
Three terms in the House, two in the Senate. Eighteen years is more than enough time for anyone to hold that much power.
A nice side effect would be more people working hard at the state level rather than seeing the state legislature as just a stepping stone to national office.
So I don't know where you got 18 from!