I think that it would be neat to have something like coloration or structural changes when you upgrade your robot. e.g. when you get the bow upgrade, you get the mark one archer eye scope. Another example: when you upgrade arrow block, your sword changes color.

I think that this could be a neat feature, and it would make sense... but it is not necessary. I would focus on gameplay before aesthetics. Still, I hope this ends up being added!

yes, cool ideas! Could also do things like the jetpack not being part of your back until you upgrade it.

Might visit this if I get an urge to polish things up!