You do save about $50 on a renewal for a regular AP. You can purchase a renewal voucher in advance of your expiration date (call the pass holder phone number). Usually I do receive a renewal reminder...but there have been times that I have not.
Also, if you will be renewing your pass in person, you have a 30 grace period after the expiraton date (also call to verify this, but it has been an "unwritten" rule for the last few years). If you do renew in person after your expiratrion date, your new pass will be back dated to expire one year from the expiration of your old pass.