Gail's got it right!
The only perks are...doing it in one step, and the little things like a "branded" lanyard (booking through WDTC it says "WDTC", booking through Costco it says "Costco", and so on), a little pin that most people trade with the CM who hands them the pin, preferred seating vouchers to things like Aladdin (we went at a quiet time and those actually caused us to wait in line longer and our view from the "orchestra" section was worse than if we'd sat back farther with the normal folk), and then a voucher for Mickey's ToonTown Morning Madness (gets you into ToonTown an hour earlier than most get into TT, they have a tiny parade, and you can get a leg up on autographs or riding Roger Rabbit or the Go Coaster). Those little perks aren't worth much to some, and are worth a lot to others.
For us, MTTMM was good to experience, but I wouldn't pay more than 5 or 10 dollars per person for it (and not until there's another person in our family, if there ever is). Our lanyards aren't used anymore, as they are wide and itchy, and we wanted Disney lanyards. Only I kept my pin. etc etc.
For you it might be perfect!
Also, there have been some that, depending on when they are going and where they want to stay, have found that the packages are the same cost or better than what they were finding. YOu just have to do the research on your own exact trip to find the answer for your situation!
Have fun!!!!!!!