Someone already mentioned a class system and I personally think it would add a lot.
Specifically, Classes being their own separate characters with different personalities. Each one with a set of their own strength and weaknesses tailored to specific playstyles. Perhaps one that focuses more on stealth, being harder to detect and a little faster but losing more coins when caught and having a larger speed penalty when at larger sizes. Another could be a larger kobold who can carry a lot of coins with less speed penalty but is far easier to detect. Maybe even a blueberry one with a bonus to all stats but slowly gets larger as time goes on.
(This next part may be hard scope wise) If you wanted to add to the game's overall playtime till full completion to you could have each class possess their own "completion percentage" as well. Each class requiring things to be done (as that class of course) that further that percentage. You could even give rewards to the player for reaching a high completion rating with a character (maybe a large reward if all are at a 100%). Anyways sorry for the mile long comment but I hoped some of these ideas helped. :)