I hope everyone stays nice and even in terms of abilities, if you allow some form of stat boosters and only a few groups of folks get them it could be that much harder for a newer player to get there because they now have to deal with a squad that has the better stats.
Not an easy thing to do, so if you do add this idea make it somewhat fair, a small speed boost or a few more health after reaching a certain rank? Nothing that goes overboard though! Maybe two or three rank bonuses at most sounds very fair to me.