It is certainly true to say that something is only worth what someone else will pay for it.
But perhaps putting too much emphasis on the work that goes into something is a bit like looking through the wrong end of the telescope, it's the perceived value of the finished article which largely sets the price.
As far as art in the form of paintings is concerned the amount of time spent by the artist is not always very relevant, value is determined by who the artist is, the skill level demonstrated and probably equally importantly, whether the artist happens to be in fashion at the time. Fortunes have been gained and lost on the latter!
The market for model boats is currently rather in the doldrums. There is very little upmarket demand except for items such as builder's models and those with particular historical provenance. The models of the late, lamented Brian King did not fetch very high prices last year despite being some of the best examples you could possibly find in terms of craftmanship. Not all of them sold either.
I did the Caldercraft Imara review in the early 1990s. The model was too big for me and I sold it at Christies for £1,200. You would be most unlikely to get that now even ignoring the effect of 25 year's inflation. Apart from going out of fashion (see other topics on Museums putting their models into storage), I think that another reason for today's low prices for model boats is the availability of high quality kits. Almost any reasonably competent modeller can put one of these together to a standard that would formerly have been considered 'museum quality', and of course many do exactly that so there is little scarcity value.
With original paintings, buyers can be sure they are buying something unique (although too many prints can depress value) but anyone buying a Model Slipway Aziz should do so in the knowledge that there are probably a hundred or more similar models out there built to varying standards, some of which are likely to be better quality than theirs. They may have purchased something that will give them a lot of enjoyment but there is little intrinsic value in the accepted sense as the item is not scarce. Buy a decent painting and you may have a family heirloom to hand down to your kids. Buy a decently constructed kit and it might well just be binned when you fall off the perch! Your heirs won't get anywhere near what you paid for it and will be lucky to find somebody to take it off their hands.
Colin