I often use wobble boards when I'm doing CF work. One of my favorites is to do unilateral DB snatches on the wobble board...it ratchets up the difficulty (and the benefit). I've also taken to wearing a weighted vest when doing bodyweight exercises.
Strictly my opinion...but I believe that once you're sure your form is good and you've reached a high level of competence with the bodyweight stuff, it's a good idea to find ways to make things more difficult. I think that you can reach a point of diminishing returns where there's limited benefit to going faster...and that you're better off increasing the challenge at that point. Maybe go "free" occasionally to expose yourself to the high speed, but not every time.
Just my $0.02