Being able to book at the 11 month window at your home resort...being able to book at other resorts in the system at 7 months. Having access to the Disney Collection, World Passport collection and Adventures by Disney on points... There are a few minor perks like 10-20% discounts at specific restaurants ( they change frequently), and the best non-point perk...$100 discount on APs. You also can park free at valet lots that are attached to some of the DVC resorts and all normal on-site perks.
Don't forget about the DVC golf membership if you are so inclined. I saved $100 for myself on ONE ROUND in May! Costs $50 but dumps the price as low as $35 a round.
Access to DVC member-only pins, 25% cash bookings on DVC hotels, discounts on ticketed events such as Mickey's Not-So-Scary Halloween Party, Mickey's Verry Merry Christmas Party, Pirates & Princess Party. DVC member only sneak previews of new attractions. Access to the Disney Cruise Line Member Cruise. Discounts on annual passes.