If your device uses more than 100mA, you will need those data wires. For a USB port, a USB device is only allowed to draw 100 mA until it asks permission from the host (using the data lines) to draw up to 500 mA. From a charger, the charger has resistors connected to the data lines, and the configuration and resistance of those resistors tell the device how much current it can draw from the charger. Without those data lines, a well designed device won't draw more than 100mA.
Using thin wires is a problem, especially when those wires are long. The voltage drop across the wire follows the equation V=IR where I is the current drawn, and R is the resistance of the wire. The resistance of a wire is proportional to the length of the wire, and inversely proportional to the crossectional area of the wire, and the crossectional aria is proportional to the square of the diameter. Halve the diameter and you quadruple the resistance.
With a switching power supply in the device, the power drawn is constant. Power follows the equation W=IV (watts = current * voltage). If voltage drops, current has to increase to keep the watts constant. So the more resistance in the wires, the more power is dissipated in the wires. Eventually, the amount of voltage drop in the wires will cause the device to malfunction.