Are there additional benefits to fielding max-rank soldiers?
One of my soldiers is rapidly approaching Colonel, the highest rank. Once he gets there, is there any incentive to keep bringing him for missions, apart from the obvious advantage of having a strong soldier on the field, i.e. will the additional kills advance him in any way?
As far as I know, once your soldiers reach Colonel rank, they no longer advance (unless you count Psi training as advancement, but as far as I know, that has nothing to do with killing aliens in the field). The only advantage of having elite soldiers is the fact that you have elite soldiers on the field - more powerful, higher HP and more perks.