I agree. We used to do line drills all the time.
As I'd mentioned elsewhere, my original dojo was a high school gymnasium. So we did all sorts of things with that much room. We did sprints, spin drills, various combinations, whatever.
We would also sometimes take advantage of the painted border of the main gym floor. We would work on slide-through or spin techniques or various combinations, then check to see if we had ended up as we were supposed to in relation to the painted line.
We also did all of the above blindfolded. It's funny how discoordinated even martial arts students get when they close their eyes. We used to do a lot of things to wean ourselves off of being so dependent on our eyes, such as blindfighting, the aforementioned drills, walking beams at various distances off of the floor (which is more perceived balance based on visual height than real balance), and jumping backwards up steps with our eyes closed.
I think that constant and consistent work on the desired principles, introduced with as much variety as possible, is a key element of stimulating growth, maintaining interest, and retaining quality students.