In regard to the original post, I cannot be sure, as I am no longer interested in following the machinations of the insurance market, but I suspect that Towergate may have simply withdrawn from the dinghy insurance market, or Merlins.
You need to be aware that most insurances, including Craftinsure, are not "new for old" such as in the case of most household insurances.
Dinghy policies are underwritten on an indemnity basis. This means that settlement will be net of an allowance for wear and tear. In the event of a total loss, the most you will receive will be the market value of the boat and accessories. Insurers are generally pretty fair when it comes to loss of masts and often do not apply much deduction.
In practical terms therefore you should insure the boat, its trailers and spares, on the full market value basis. But insuring for the new price will mean you will be paying excess premium for nothing if the boat and kit, is not new.
So far, so good, but the Craftinsure wording also states:
"We will pay the reasonable cost of repair for loss or damage not exceeding £10,000 [sic] Reasonable replacement or repair may not result in the appearance and condition being the same as that prior to the claim. In the event of total loss or constructive total loss, we will pay £10,000 or at our option, provide a replacement boat of a similar age, size and type."
Notwithstanding the dodgy punctuation and frankly syntax, in what one might hope was a carefully checked document, there is thus a limitation. In the event of a total loss of say, your as new Merlin, Craftinsure appear to be restricting their liability to £10k, or "at their option" finding you a replacement boat. Given how discerning most Merlin sailors are known to be, you may not be happy for Craftinsure to go this route even though, you have no say in the matter. There would, I fancy, be plenty of scope for "discussion".
Personally, I find this clause un-nerving. Some Merlins are worth more than £10k, ours possibly included. Even older boats, with multiple spare masts and spare sails, rudders etc, will exceed that market value. While a total loss of all this kit may be unlikely, in the event of say, a garage fire with your Merlin in it, it is not impossible.
I might add, that neither Craftinsure nor Noble carries any penalty for underinsurance. In theory, one could be tempted insure the boat on a lower sum insured, based on what you think, a "worst case scenario" might be.
I do not recommend this. Insurers are notoriously sticky when it comes to large claims especially if underinsurance is a feature. While neither insurer I mention has given themselves any protection against people who deliberately underinsure, they have many and varied ways of being obtuse when it comes to a claims settlement.
For example, one might, either by design or neglect, insure one's £15k market value Merlin (inc spare masts) for £7k. In say, the loss of some rigged masts and new champs sails plus accessories such as spin poles and fixed rudder, value £7k, the insurer might attempt to argue that the boat is thus a constructive total loss. And they are entitled as a result, to retain the salvage of an undamaged hull which escaped damage. They might then try to sell the hull back to you for, for example, £4k. Such largesse.
I know this possible because I have seen it attempted by a dinghy insurer. Far better to insure the boat, AND accessories including spare masts, rudders and paraphernalia etc, for the proper full market value.
For the record, I dealt was a Chartered Loss Adjuster for thirty five years; which fact I do not generally like to advertise. Nevertheless it is the case.
I insure our boats with Noble and have done so for years for the type of reason I have illustrated above. Noble are generally pretty fair even though no doubt, as with all insurers, they may have their moments. Noble have been owned by RSA insurance since 2011. What you might lose in personal service, you gain in a dispassionate approach and unimpeachable security, I think. Premium alone, is not the only metric.
I have no direct experience of GJW or Aspire etc, nor have I reviewed their wordings. They may well be fine.
Make of that, what you will.