I have $5mm umbrella, even though NW is higher. I just think the risk of litigation that costs more than $5mm (plus my underlying auto limits, if the claim is auto related) to defend/settle is very low.
I do think there is a relationship between NW (or, I guess I should say, the value of non-exempt assets) and umbrella coverage levels, in this sense: If I had, say, $750,000 in non-exempt assets, and I get a $5 million judgment against me, I can always file a personal bankruptcy case, give the trustee the $750,000, and discharge the remainder of the judgment (assuming the judgment is not within the category that is nondischargeable). So all the coverage I would need to protect my non-exempt assets and avoid having to file bankruptcy would be $750,000. But if my non-exempt assets were, say, $5 million, then absent insurance coverage, I could have to give $5 million to the trustee, to get a discharge, so I have more NW to protect by insurance.
I am not saying umbrella coverage should equal NW or non-exempt assets (and I am sure as heck not giving anyone legal advice; I am not qualified to do that!), but I do think the amount of NW (or non exempt assets) is relevant to the decision about amount of coverage. And I guess, now that I am typing this, maybe I should increase my coverage levels....