Umbrella policies are cheap, so there is no reason not to.

In fact, what I have done is reduce the liability on the autos and the home as much as the insurance company will let me (which still ends up as $500K on the autos and $250K on the home), and pick up the slack with the Umbrella policy.  The liability coverage under the Umbrella policy is cheaper than it would be under the home insurance and auto insurance, and you can get more coverage with an Umbrella policy.

 $5 Million coverage with an Umbrella policy is what, $700 per year or something?  Might as well do it.