Stacy, it is entirely up to you what value you put on anything. If you are getting rid of a stamp set, look at it and imagine how much you could sell a used stamp set for, and assign that value. However, if you actually sell it, just use the amount you received for it.
Chautona, I admire your restraint! I usually end up going in the hole....I don't actually 'earn' the money before I spend it and then end up trying to catch up. It's not strange at all that when you spend more money, you often make less cards. Time spent perusing galleries and store web sites, as well as actual shopping in person, takes away from card making time.
Glad to have you both on board for this coming year. I will be posting a challenge next week, to get the new year started. (inspiration challenge, not an organizational one)