Nah... the M3 is doing just fine. Leave the M3 be so that it is fragile, needs protection, and is dependent on its speed.
Now, if the proposal were for the Sdkfz 215, then I might go for it since all that is used for it to pummel cities and other strats for the omnious "bombing percentage" in the gv scoring category. Most dont realize that the 251 has (what seems to be) about triple the armor on it vs the M3. When paired with a bunch of tanks and wirbys there is no reason to take the M3 but yet it is knee jerk reaction to do so.
The 251 has the armor, the M3 has the speed.