The differential mode gain is $A_{dm}= -hf_e*\frac {R_c}h_{ie} $ So from this we can see that Re is not related to the differential mode gain so if the value of Re is large there will be as such no effect on differential mode gain.

The common gain mode is $A_{cm}= -hfe*rc/(hi_e +(1+hfe))*2R_e$ So as we can see that commom mode gain is inversely proportional to the commom mode gain so with increase in the value of Re, the value of the common mode gain decreases.