That is actually in place (it shows as "(+N)") and you get one extra score for every 4 consecutive full line. I think the negative points you can get are not a great decision by me and I removed them in the post-jam version. Now the score is not about rating your performance, but just to give you an additional sense of (albeit meaningless) progress and achievement. i.e. it's way less of a value judgment of your play and I think that fits better!
A great thing about making such a simple game is that you can take the time and make it pleasant and just sprinkle in a bunch of stuff that looks cool. My music person is well aware of the praise people have been giving him and I am very thankful to his contribution as well!
And there is a post-jam version already up on GitHub. There are no grand changes, just gamepad support, audio/music mute, IJKL as an alternative to arrow keys and a really cool zoom-out when you press escape! I guess one could put in more (so that it will seem pseudo-infinite) gimmicks to discover at larger heights, but otherwise I am not sure what to add that would really fit the theme of it being a relaxing experience. I'll think about it and see if other people suggest some other clever things!
Thanks a lot for taking the time to play and for writing such a nice comment :)