I don't think a soft touch valve will stop your RSI because you're still doing the same motion repetitively, but it might make it a bit more liveable with. I suffer badly from it in my right hand, wrist (jokes please) and shoulder. Have one wand with soft touch and one without, doesn't make much difference but the soft touch is maybe a little better over a long day.
Simple answer - if you can't get a soft touch valve for your wand, change to one that has!! The westpac wands have them. I know Mike says he's had trouble with his but mine has been perfect for 2 years hard use (kiss of death on myself there now!) As long as you carry a repair kit with you for peace of mind, no problem. If something keeps failing regularly, you'd have to look at the working conditions of the wand to find what's causing it because that isn't normal.
If regular valve component failures are happening they can't all be dodgy parts, it's either excessive heat (doubt that , mine has 230F through it regularly), frost damage or chemical degradation