Nine-speed will be around for quite a while, there are still plenty of bikes being sold with 9-speed as standard. The extra gear is relatively trivial in my view. As for the chains, in theory 10-speed are just as strong and durable. Which means it must just be dumb luck that has caused me to snap two chains since getting a 10-speed road bike, having never snapped one before in well over thirty years of cycling...
If I were you I'd save my money and get the 9-speed.