Stats
Besides the system itself, stats of the spell will need to be adjusted very carefully. Since you would be invincible against single-target spells as well as deal damage by reflecting them, this is an extremely powerful effect, so we would not be doing exactly this. We would need a good amount of time to test and balance this just right.
Simple balancing solution:

Fairly high MP cost, moderate recast time (difficult to maintain over long periods)
Provides % chance to reflect (rather than every spell)
Wears off after certain duration (2-5 min max) or certain number of spells (e.g. 3-5) are reflected.

Most enhancing magic spells are relatively low cost with relatively low effects for good durations so it would be interesting to have a more powerful and costly enhancing effect.