Read an article about this sort thing a few years ago. It was more about books in general rather than cookbooks specifically but was rather thought provoking.
If you have a large cookbook collection the reality is that 99% of them are worthless financially speaking. Charity shops might want the newer ones but the rest are too big and bulky to store for extended periods especially as they might only fetch a token amount each. Selling on ebay is for most books not worth the effort.... usually postage is more than the value of the book let alone the time and packaging costs... 500 books anyone?
Most collections are a labour of love personal to the individual collector. Do you want to be given Uncle Tony's collection of 5,300 different beer cans or matchboxes? The sad reality is that family will take some, some will be sold and others will be given to charity but I suspect most will be pulped.