Sorry your trip was disappointing but Carol and the others have good points.
Sometimes disappointments are self inflicted. Disney does not control what happens to a guest prior to arrival. Bad flights, delays, lack of sleep, tired kids, illness, are completely out of their control.
Why were you not able to list your party on Dining, did you call Member Services at least 2 days prior to your arrival and have all 8 members of your party listed for the dining plan. If not, then that is a not a complaint you can make. If you booked the Dining Plan for all 8 members of your group at least 2 days prior to arrival with Member Services and they messed it up, then Yes you have a complaint with them, not the front desk at the WL.
As to waiting, depends on who messed up the dining, you or them. As to getting a room prior to 4pm that is something that many guests get upset about and truly have no right to. Regardless of how tired one is, or what one plans to do arrive one arrives, rooms are not guaranteed until after 4pm, so everyone needs to plan accordingly.
Seems that your trip was more a case of just bad luck then major complaints with DVC. I am sorry you had such bad luck with illness and such and that really clouds the issues at times.
I would hope before you write them, you would re-evaluate what was actually their short comings versus your own personal situation.
Hopefully your future trips will be better.