I've been using/abusing/collecting Spydercos since 1990 or so and I like Spyderco for a number of reasons.
First there is the cost factor, they give you alot of bang for the buck!
Second is collectibility - there are so many varieties, some very similar, yet radically different, not just blade coatings or handle material either...look at the differences between the Spyderfly, civilian, Meerkat, Persian, Salsa, Karambit,and Gunting...although there are similarities each and every knife offers something new. That's what keeps me coming back!
Third is reliability...I currently own about 25 Spydercos and have owned over 60. 3(Police, Provenator, and Viele) I destroyed through usage, 1 was confiscated at an airport(Ayoob, forgot it was in my pocket), about 10 or 12 I've given as gifts to LEO and military friends who needed something right away, as well as a DiveBar that went to a friend who wanted a different type of dive knife. One(Co Pilot) I used to bribe a customs official in Central America with. The rest I traded for other knives/gear and I actually gave a guy a delica because I had no cash on me to buy lunch at a Chinese takeout place, once!
Fourth is the company's contributions toward the Military and Law Enforcement Communities.
Fifth is their customer service...I only had one problem with Customer Service...I sent an orange handled rescue and a plain edge civilian back and they were stolen in the mail, I neglected to insure the package and was SOL. My only gripe was that they would not send me the part to fix the civilian, myself. I needed a new clip (rubber wore out on mine)and they insisted I send the knife. This was about 8 or 9 years ago. Since then, they've sent me clips, screws, etc without question/hassle/charge whenever I have asked.
I could go on and on...they make great knives, stand behind them and aside from making them "tear-down" proof, I love them. My EDC knives are usually 2 or 3 custom blades, but I always have a stainless delica or worker in my mission wallet and even use a cricket as a money clip as well!