Also note that the "value" of a pin can be quite subjective. For example, many limited edition pins found at WDW, for example, are highly sought-after if you bring them to Disneyland, regardless of what their values would be last listed in the Disneyana book. The same can be said about Disneyland's limited edition pins when one brings them to WDW. I discovered this first hand during my last trip to both.
Cast lanyard pins are also hard to value in terms of their desireability. Again, they may not fetch top dollars, but for pin collectors who are in this not for monetary value but for collection, these are usually highly collectable and sought-after.
To be, the best place to know if the pin you have is "valuable" or "sought-after" is to ask the pin traders at the park when they have their pin albums out. Most will tell you truthfully if what you have is highly collectable - they may even ask if you'd like to trade with them if you have one.
Zz.