Looking at the evolution of a character like Micky Mouse you can see in proposhion size and character he has not changed much at all, i think this is because Micky mouse and his popularity has make him more of a fashion accessory and a mascot rather than a character who can develop.
with age all Micky Mouse has gained is gloves at the start to help his black and white animation and latter,more detail in his drawings with shading. Witch is natural as our TVs and animation programs advance in quality also.
The character is now stale and uninteresting. and as this is has came on hard times as Disney try to change there mouses aperince the audience rejects its change. For example, in 1955 Disney made a TV advertisement with Micky Mouse in a modern style animation.
The cartoon was taken off the air not to long after its relece because fans of Disney claimed its style to be to communistic.
Apart from changing Micky Mouses style thy have also tryed to improve his personality. Thet have done this mostly throw there games rather and television as this is a new market.
this has been been mixed waters as not every one enjoys this new personality of Micky mouse.
It is something that i personally don't believe can develop much further because of the constrained of fans and there character, What people like and what people are use to is very diffident and difficult to deal with.