golok, I am not sure if the following is of interest, but I shall post here and hope others will join in.
Firstly, if you are interested in "rich & interesting history" a few other companies to consider/learn about are : Remington, New York Knife Co., Cattaraugus Cutlery Co., Utica, Robeson Cutlery Co.,Camillus and Winchester, amongst others. Generally, the first 2 fetch the highest prices followed by Case.
Value is important as it is determined by demand and supply. If I am uncertain about a particular model or knife, price will determine how much it is in demand or hint at the quantities available. Many of these knives in near mint condition should stay as such and it is our responsibility as collectors not to use them and maintain their state so that we can "share" the pleasure of ownership with others later on. Naturally, appreciation in value implies that correct decisions were made in our earlier purchases and encourages us further whether we sell the knives or not.
My advice to you is to read as much as you can on Case knives (3 good books are Antique Knives by B. Voyles, Case Classics by J. Parker & B. Penley and one that I don't have is I think called 100 Years of Case Collecting), go to America and visit several shows to learn as much as you can. Not many sellers will let you handle their older, pristine mint knives, and knife etiquette suggests that you do not handle knives that you really are not that keen on. Operating the locks will usually cause blade rubs/scratches and frowns on the sellers' faces. Sellers will have to wipe off every knife you handle and you don't want to be unpopular that quickly! You can also increase your knowledge by studying Case knives sold on ebay (pls don't buy anything) over several months and chatting with the sellers. Price will indicate which models are hot currently.
Offhand, earlier stamps are better made (Tested, XX, XX USA, followed by 10-dots) and handles of Pearl and stag (green and red, also second-cut) are greatly in demand, followed by greenbone, bright redbone, dark redbone followed by the manmade materials. Blades & springs of hi-carbon steel fetch more than knives using stainless. Regarding what to collect, some go for models within a particular time period, some collect stag-handled or pearl-handled knives, some collect patterns like Trappers, Whittlers, Congress, Scout, etc. while some go for the extraordinary/rarer models (John Carver, Bill Boatman, dog grooming blades, fish knives, Hawkbakers muskrat, and other mysterious patterns). Easier to find and easier on the wallet are the models made after 10-dots (1970), commemoratives, Classics, SFOs, etc.
Recently, T. Bose collaborated with Case on a range (its still being continued) that is quite nice with blades made of ATS-34. You might like to look at some, but I do believe that their rate of appreciation over 10 years will be nothing like that compared with Testeds and XXs. Collectors want minty knives made to be used (which were not), not collected.
Two other points which I would like to mention are : Go for quality not quantity ; and beware - many fakes out there and knives that are not what they seem...
Whew!!!
Sazabi