Surprised at allowing 50% uplift - 10% is normal here without a strong justification. I am going through this now with my project boat, which is already insured for more than I paid on the basis of a surveyors valuation. I am spending more than the purchase price on the refit and when it is finished I will submit the bills and a final survey inspection to support an increase to the top market valuation.
With my Bavaria 33 I insured for the new price of £105k in 2015 and thought of reducing it last year until prices went mad - I sold it for a little under that value so good decision to keep it the same.
Is it worth increasing it? Yes for 2 reasons. First it is cheap. The premium for all risk element on these sorts of values is around 0.3-0.4% - so an extra £10k costs around £35 per annum. Second if your insurance is agreed value (and not market value) you know what you will get if the boat is a write off, and perhaps more important a higher value means a higher limit for repairs before they consider a write off. With the cost of repairs rising probably faster than boat values this is an important consideration.
Insurance is not really about risk, which for cruising boats is extremely small, but about how you view the consequences.