Dennis,
The question about when to change shocks and what the replacement should be is very subjective. Some people expect new shocks to make the coach ride there are no bumps in the road. This is of course an imposable accomplishment.
You say that your coach recovers quickly from a large bump, so the question is how much more rebound control do you want? If your shocks are to stiff (very high rebound control), your ride will be harder (more abrupt) when you hit a large bump, although there will be no porpoising after the bump. So you will need to decide what you are trying to accomplish with your coach. Koni shocks are firmer than Bilstein shocks so if you want more rebound control, they are a better choice, although they are more expensive.
You should check your shocks for condition. If one is leaking oil at the shaft seal, it is bad and should be replaced. The same thing applies if one has broken or damaged mounts. However is none of your shocks are leaking or broken, and you replace them with the same shocks that you now have, you will probably be wasting your money, because you will not be able to tell a difference in the ride.
My 2000 Marquis (11 years old with 112,000 miles) still has the original Bilstein shocks and I have no plans to change them because they are still performing very adequately. So what I am saying is that shock replacement has to be the owner's call, according to the condition of his shocks and the ride that he wants.
Gerald
