I've done both and the 7 hour one is much better. As of this past August lunch was still in Mama Melrose's and it was very good. It is an all you can eat family style meal with loads of food and yummy desserts! One of my fav parts was going behind the scenes at the American Adventure in Epcot, really cool! I also really enjoyed the Keys to the Kingdom Tour. Lunch was at Columbia Harbour House and you picked what you wanted at the start of the tour. On both tours, they have everything ready for you when you arrive at the restaurant, real nice touch. I think a lot depends on who your tour guide is and how many people are in your tour. I've been very lucky and havehad wonderful guides and not many people in my groups. Yes, there is a DVC discount, same as AP discount. I have used both. IMHO the tours are worth it, especially if you are a huge Disney fan like I am. It might be easier to take the Keys Tour first and see how you like it and then some other time in the future you can do the Behind the Scenes Tour. That's another great thing about DVC, you know you will be back and can plan so many different things for future trips.
Have Fun!!