I personally like the idea of increasing the storage as an additional option after 100. It is not too strong, but some nice quality of life.
Maybe even some small quest rewards like a few ressources or an adventure point could be nice, say every 10 levels after 100 or so.
An additional Hero after level 100 would be quite a big change and very strong for offensive players (def-heroes often dont reach high levels as fast). I would like that aswell, but i think it is quite hard to balance. It opens up more possibilities for the late game, where multiple hammers for bigger players is not unusual.