I just bought a brand new 2019 Honda Ruckus 3 days ago. I love the bike and have already put in 70 miles of riding so far. When I put my Ruck up on the center stand I noticed that the rear wheel does not move on idle.

When I completely release the rear brake adjustment, the wheel spins freely, so much so that it feels like brake pressure is being applied normally.

I can spin the wheel with my hand but I cannot achieve even 1 full tire rotation when letting go. If I loosen the rear brake any more there is too much freeplay in the handle and it does not feel safe to ride.

I have an appointment with my dealership about this issue on Monday, but I don't want to waste their time if this is normal behavior. When I significantly loosen the rear brake it feels like I have snappier acceleration, but that could be mental. Is this a problem, or am I going crazy?

 

This will go away as the brake shoes wear down. After all, it is a brand new bike and needs time to break in. DO NOT loosen the brakes too much, that's not safe. Adjust them so that they still function.
Me personally, I would not go to the stealership for this unless it was free. Just my opinion.