Got a better idea. Gladiators having reached a certain "veteran" threshold, say 2000+ fights, to gain access to an item which improves their attributes in some way. This can finally put these 4 little square slots to use. Additional item of that kind can be rewarded for each 500 or so extra fights. This will keep the old dogs in the game for quite some time even if Nate decides to introduce new super-slaves every few months.