I'm a little confused by what you said about "not being able to charge while already walking", because you can only start charging while walking. If you press the button while standing still you just do a headbutt. Regardless, I've changed it so that charge has a bit more oomph to it. You build up speed slower than normal walking, but you have a significantly faster max speed (faster than dive). I also changed dive to work like it did in the previous games. So if you don't want to wait for the slide to finish, you can just jump.
One other fairly fundamental change I made, which should make the game more fun is I removed the top-speed limit and added a speed increase cap. By that I mean, speed can exceed any number, but you can't increase it further beyond what you would normally be able to. So when you jump out of dive, you'll keep your dive momentum even though you aren't diving anymore. This is a pretty standard thing in these kind of games, but it wasn't in place before now. I won't be changing the demo, but all of these changes will be present in the final release (unless I change stuff again).
Really appreciate the in-depth comments!