Bands might help with the speed/power aspect.Initially an instructor told me (many moons ago) that doing kicks with ankle weights would improve the speed of my kicks if I did them in an explosive fashion, but after trying it a few times I ditched the idea due to pain in the hips, knees, ankles etc. Also I noticed no increase in speed, just increased injuries (it's difficult to control some kicks done fast if there's a weight on your ankle!)
Although not on a regular scheduled basis, I started re-incorporating ankle weights back into my training always performing exercises in a slow controlled manner to improved the strength in the muscles that enable that particualr kick to gain/maintain height as opposed to speed/power.
I came across this after practicing with bands on the advice of the kinesiologist who helped me rehabilitate my hip injury. The benefit shows up when I break boards.
You see, bands increase in tensile weight the further you stretch them. That means that you are extending with greater force at the end of your kick. Take away the band and this translates into extra snap at point of contact.
Cindy