I did end up taking the plunge also, and got an annual plan with worldwideinsurance.
(Un)fortunately I won't get to sample their claims department this time round, but in light of their assurances in #4 I booked through without CDP inclusion, making sure to get a vehicle < £50,000 in value.
(Un)fortunately they upgraded me due to a car shortage, and I ended up with something worth £70,000 in their books.
Hertz insisted that, despite it not saying so in their paperwork, that since they upgraded me the value will be capped at what I had booked. It makes sense (and would be unfair otherwise) yet I wasn't terribly convinced by their delivery.
Something to remain aware of, perhaps!