Having been extensively on computers for the past 25 years and I have never experienced the whole keyboard-/mouse-pain thing even in the slightest on myself. I know many collegues who did tho.
I wonder whether this has to do with me being a bass and guitar player. Playing an instrument where you essentially press down thick steel wires with your finger tips with full force, while your fingers are in odd angled ("unhealthy") positions for hours certainly does something to your motoric system.
I know anecdotal evidence with n=1 is useless, but the idea that motion is important to reduce body pains isn't exactly new or unresearched. A whole family of ergonomic chairs have evolved about that very idea. I know multiple people whose only solution to excruciating back pain was simply to exercise and build muscles in the back, and they tried every ergonomic chair in the book. The only thing that really helped was excercise.
Since I don't have RSI take all that with a grain of salt, but maybe trying with those guitar-finger-strength-trainers for a month isn't that big of an investment?