Make the game into whatever you would enjoy playing yourself! Even if you don't want it to be a simple story-focused visual novel anymore I will still play it :D Just make sure to set realistic expectations and don't feature-creep! Otherwise you might burn out quickly.
I think its a good idea to go a bit more lighthearted on the themes of the story but still keep the core tone as a serious emotional drama. I'm sure you can pull it off, as the jam version already was kinda like that!