Having done my moderator bit by updating the title and moving the thread, I will take that hat off and put on my Paperweight Collector hat.
As Sue has said, there are some places to look for general confirmation on Caithness and Paul Ysart weights.
The GMB has a number of members who are also paperweight dealers, and perhaps some of them may contact you directly or may post a reply here with their own advice or questions.
Regarding the 2003 insurance valuation, that sounds as though the 50+ collection has mainly good condition "collector" items ranging from, say, £100 to the £550 upper figure. As you are aware, that valuation will have been higher than the then current "resale valuation" which is what a dealer would be considering.
Selling a whole collection through a dealer would provide less than the current market valuation (as agreed by the dealer). In general, some dealers would look to pay up to around 60 to 66% of their estimated market value. But as you have said, that needs to be balanced against the work needed to sell them individually yourself, either through eBay or similar, or perhaps through a local auction house (where fees can be quite high these days).
But what about that £7,000 insurance valuation of 2003 - would it be higher or lower now? In many cases, Caithness weights do not make the sort of money they did some years ago. On the other hand Paul Ysart weights have tended to at least hold their value with many showing a reasonable increase, and some, in the past few years, changing hands at unexpectedly high amounts.
Lets see what others have to say.