Renown is a great currency system, but a lot of longtime players will reach a point where they are just stockpiling them because they've already unlocked all/enough units to suit their needs. I know there are going to be more units unlocked, and more things buyable with renown, but eventually people will have bought all of them and will not have any use for renown anymore.
Should there be a cashsink that you can continually pay renown into for a temporary unlock? What sort of features should be temporary unlocked?
Should there be a secondary currency/XP system that you gain or level so you can keep achieving something after you have no use for renown anymore?
I've also reached this point where I have each rank of units and multiple copies of each rank. I know most of the fun should come from playing games, but a lot of people like a continually progression system or feeling of earning something worthwhile. Just my thoughts