Only a simple "offline" highscore, because an online highscore is much harder to make. With a highscore, the player has always a goal(to get a better score, than his best score). A goal for the player to follow is really important for these kind of games. That´s a basic Game Design Rule. But it´s definitely something different to now the Game Design Rules then really having the time to implement all of the features in the game. Believe me :D

,,I wanted the player to suffer from low energy! :-P". Yeah I know, but the problem is that because of the small amount of energy you get from them, there´s no motivation for the player trying to get these blue things. Right now it´s the better tactic to just never try get one of these blue things. I would reduce the energy as well as making the time you need for getting you´re energy automatically back longer and making the amount of energy you loose for moving bigger. And then I would make the amount of energy you get from these blue things bigger.