Unfortunately, we now have extremely uncompetitive elections, and I wonder if this is such a problem in parliamentary countries. House members (and, I suspect, state legislators) are routinely re-elected at 90%+ rates. Even Senators, who can't benefit from scientifically precise redistricting but otherwise reap incumbency's rewards, get returned at rates in excess of 2/3 of the time IIRC.
I seriously wonder whether political competition is dead in the legislative branch. Lately I have wondered whether the bitter divides over Presidents are in part a function of the fact that Presidential contests are about the only democracy we have left.
I wonder what incumbent reelection rates are in other western countries.
Senate seats are more up for grabs than House seats, although you're absolutely correct about the power of incumbency. It's inexplicable to most of us why Louisiana has never elected a Republican Senator while reliably voting for the Republican presidential candidate. Still, it does happen more in the Senate as both Max Chambliss and John Ashcroft can attest.
I do not know, but I'd be willing to guess that the power of incumbency does not play such a pivotal role in other western countries. The money isn't as big a factor, for one thing, and the variety of parties to choose from is far greater. Under most parliamentary elections, voters must choose from the survivors of the first round, neither of which might be from their preferred party. That's simply not the case here.