How many d23 pins come out a year? Are there any other special perks?
If you are in it for the pins then don't bother. The only good pins to come out of D23 are the ones from the D23 Expo (every other year) and from Desitination D events (the years they don't do the Expo). You can always pick those up later, if you have patience, for about the same as they sell for new. Or, you can make friends with someone who is a member for the other perks and have them pick up the pins for you.
Outside of the pins it really depends on what you're looking for.
If you live in CA the other benefits are great! There are movie screenings, tours to the archives and studio and other gatherings. You also get priority tickets to the Expo and only D23 members can go to Destination D. For those into Disney history these are great events and well worth your time/money. (Dick Van Dyke is giving a concert at this year's Destination D! It doesn't get much better than that!)
I live in Colorado, so I don't get to take advantage of the events very often, but I retain my membership so I can hit the Expo and Destination D when I want, and for the D23 magazine. Again, you have to be a really into Disney History for the magazine to be worth it, but if you are, figure that covers most of your membership. Issues are $15 on the newsstand and members get a special item with each issue. That's $60 of the $75 you pay.
So, as with most things you mileage will vary depending on what exactly it is you are into. I'm a charter member and will keep my membership until Disney figures out a way to diminish the value so much it isn't worth it any more (I'm looking at you Classics Collection Club!).