Personal umbrella is my entire job and while I obviously have a vested interest, the easy answer is you should have as much as you can afford; it is always better to have it and not need it than the reverse. Umbrella coverage is about the cheapest insurance you can buy. The issue is you never know who you are going to have an accident with and what their injuries/expenses are going to be.
In my presentations, I use an everyday, real life, example from about 20 years ago. My client was running at the health club and clipped another runner's heel, what we called a "flat tire" when we were kids. The other individual fell and broke his wrist. On the surface not a big claim/lawsuit however the injured person was a pediatric heart surgeon making $750,000 a year. Due to the break he was no longer able to operate and had to take a teaching position at $250,000 a year. Given he was in his early 40's the lost wages alone were $10,000,000+ that our client was responsible for.
This was an accident that can happen to anyone and is just that, an accident, but the fact it was a surgeon, as opposed to a fast food worker, turned it from a nothing burger into a potential financially devastating event. The fortunate piece was our client carried a $10M umbrella and the injured party was willing to settle for the policy limit and not pursue a lawsuit.