Thanks a lot for playing the game and the honest feedback.
I have thought of adding a time limit but scraped the idea as I wanted it to be an endless runner. I'm currently working on adding different kinds of obstacles which spawns after a specific score is reached. As you said, this would help increase difficulty over time and make the game more interesting.
I have tried gradually increasing the game speed. But this turned out to make the game impossible to navigate very quickly.
And yes, I will definitely look into adding more items and collectibles, like the bonus coins you mentioned. I'm sure it would enhance the game feel and give the player a secondary goal instead of just surviving for as long as possible.
Thank you, once again, for the feedback : )