Definitely an interesting concept, and I loved the feeling of finally having others around me supporting me as I grew the objects, it really hit home the stroner together theme in a very effortless way!
I also loved the idea of the interactive main menu, it drew me right into the game; and i definitely agree that the tutorial wasn't wholly necessary.
One idea I had about the sound effects would be trying to sync them up with parts of the music; so for example when you grow one of the objects the sound effect would play on the nearest beat of the bar (or a good place in the music). I thought of this as the first plant I grew hit right on the beat and it felt amazing, but I realised the later ones didn't do the same.
With a little more world building, a background and some more juice to all the interactions (like particles/sounds when people start following you) would top off the experience nicely.
Liked it :)