I found that the tripod weight was more important than mirror lockup. I have a pair of tripods.... the old heavy one moves a lot less than the new lightweight one.... but hang a weight off of the lightweight tripod and it gets very steady. I have a eyelet in the bottom of the central collumn that I attach to the camera bag with a length of light rope.... makes the setup much more stable.
surely if it was a bit windy your bag would be swaying all over the place? my tripods pretty sturdy and there was no hint of wind in my room or shake on my floor!
The "trick" is to have the bag just touching the ground, or hung using a bungy cord. That way the tripod is pulled down to steady it and the bag cannot sway about.