The default in Sketchup is for the spacebar to do the same thing as the Escape key. For a right hander like me, I tend to have my thumb on the spacebar and my ring finger on the Escape key and use the two interchangeably. But I don’t really need both options.
If I remember, with AutoCad, the spacebar is used to re-invoke the last command. This is extremely useful and saves a lot of dancing about the keyboard. But AFAIK, you cannot designate the spacebar to do that in SU.
I am posting here in case anyone knows a way of achieving this. If not, perhaps I should move this topic to Feature Request?