It's probably not advised,but I've been kegging for a year now (although I've only had most of my kegs for around 6 months), and I've only broken down one keg and that was because it needed some new o-rings.
After I empty a keg, I typically rinse it out with hot water, and then run about a gallon of BLC through my taps and then rinse with hot water followed by starsan and I leave the keg under pressure until I'm ready to fill it and then I give it another rinse with starsan.
Once I have the keg assembled and leak checked, I don't like to take it apart if I don't have to. Then I only have to worry about checking for leaks in the parts I move (the lid/pressure release for example).
If I ever repurpose my soda keg for homebrew, then I WOULD take it apart to clean it.
I disassemble after each beer as well. Just remove the posts and tubes and clean out all the o-rings. I put it all in some boiling water and then some idophor solution while i scrub the inside of the keg. Its not that much more work really.
I take it apart as far as it can possibly go every time. Everything gets washed in Iodophor, lubed, and reassembled. The keg lube will keep your o-rings in good shape and you won't have any nasties hiding anywhere.