Does sunlight reflected off a mirror enhance the temperature of the sun-rays?

A standard planar mirror will not enhance the energy contained in the rays that reflect off it. In fact, there will be some loss of energy as the reflective surface is not perfect. There is some deduction in the light's intensity as it passes by the mirror's glass and reflects off the backing surface.

Parabolic mirrors, on the other hand, focus and concentrate the light rays on a single point in front of the mirror, aptly named the focus. Although the energy is not amplified, it will be effectively enhanced because of the additive effect that will result when the light energy is concentrated.