It's a difference between 1.5A and 2A, so you won't damage the wires.
However, you are better off sticking with the 21/5 bulbs as the higher wattage ones simply do not last very long.
They make no real difference to rearward visibility.
Be wary of the LED bulbs as well. Many of them now work great, but the sockets on the C10 restrict which ones you can fit.
The LED ones tend to have a shoulder where the metal cap normally meets the glass, and that shoulder prevents the bulb from being fitted.