This 'discussion' is both interesting and depressing.
We have been with BoatUS insurance for many years. Back in the 90's, I had a recent survey to present at the start of the, ah, relationship.
They told us that they would, randomly, select policy holders for a survey that they would pay for (and own). This actually happened to a friend of mine. He passed albeit with some upgrades required due to changes in system standards over the years -- he did the upgrades and continued to be insured by them. Other than the few noted defaults, they would not share the rest of the survey without his reimbursing them for the cost.
I believe that they may have dropped this procedure/requirement after changing to Geico.
Interestingly, I have never been asked for a new survey, and it's been about 20 years. In 2018, we installed a new drive train and I asked them to increase my coverage to reflect the increase in value of our boat (to us) and they did so based on a phone call. Note that our boat's Agreed Value has nothing to do with average pricing on lesser-maintained sister ships that are advertised sometimes.
This is with their new underwriter, and we have never had a claim with BoatUS, then or now. I just finished a complete re-fit, with new LPU paint, deck and hull. We are currently doing a new survey, and then will ask for a new 'agreed value' from the insurer. If they balk, we will have to go elsewhere.
It would be poor business of them to turn us down, tho. Since they charge a fixed % of the value for the yearly coverage and we have a good track record, they make a lot of money on our premiums. My limited experience is that good boat insurance costs approx. $10/thousand, whether the asset value is low, middle, or high.
IMHO you pick the quality of the insurer's reputation, and then figure out what it would take to replace YOUR boat (emphasis on your's and no one else's), and insure for the remotely-possible-but-not-likely fire or flooding.
The insurer just wants to reduce the likelihood of ever (!) having to pay a claim, so they want your boat to be in such good condition that they make money on your premiums ---- for them, a high value boat is more profitable than one of low value that is also more likely to cost them money.
Their bureaucracy costs them about the same overhead $ whether they insure ten cheap boats more likely to, on the average, cost them a payout, or one or two highly-maintained better quality boats with a closer-to-zero chance of ever costing them any payout.
All that said, they may still make stupid or illogical underwriting decisions about age, make, and model.
Plus, they have to maintain adequate cash reserves to pay loses beyond the reasonable control of the boat owner, like weather events and damage from other at-fault vessels.
Please keep the anecdotal comments coming. Good info for us all!