I have some ideas.
1. Ability to speed up and slow down the scrolling, or at least the ability to slow it then it auto speeds up. Joystick down for slow down.
2. By slowing it down You could maximise score on the non blue tiles, but at the same time a higher score for completing the level faster.
3. some random (or not random) death tiles in the map in amongst the scoring tiles or elsewhere.
I have a version now where I can both slow down and speed up using the joystick (so 3 speeds: slow, normal, fast), but I just keep playing in the fast speed like a racing game. 'Fast' allows you to jump longer (since the jump is the same height/duration) but requires faster reflexes, whereas slow makes it difficult to jump over holes but a bit easier to run over the tiles you want.
I think it would be better to allocate speed changes to tile colors instead, so that touching a certain tile color would speed you up for a few seconds, for instance. I'm thinking of mapping tile colors to effects like this:
01 Black: Space/death
02 Green medium: Speed duration 2
03 Green light: Speed duration 3
04 Blue dark: No action
05 Blue light: No action
06 Red dark: Slow duration 3
07 Cyan: Forced long jump
08 Red medium: Slow duration 2
09 Red light: Slow duration 1
10 Yellow dark: Points x1
11 Yellow light: Points x2
12 Green dark: Speed duration 1
13 Magenta: Extra life
14 Grey: Points x3 (or confusion)
15 White: Points x4
Distinguishing between different shades of the same color would be too difficult for the player, I think, so I suggest they produce different durations of the same effect.
A confusion tile that inverts your movement, like in Bouncy, could also be an option - perhaps mapped to grey.
Regarding death tiles, unless I introduce an energy level instead of instance death, I don't think there's a need to introduce another tile than the space tile. But some levels could have space tiles appearing randomly.