"What does that look outdated and excessive? What would you replace it with?"
name
Not clean and heavy design looks outdated. I would not use background to distinct headers:
can.Construct([name, [staticProperties,]] instanceProperties)
and properties
name {String}
I would use some cleaner way (maybe text color, look at Ember's methods/properties way)
I would also remove there exessive characters like {} [] or added some spaces - because they look really like a mess (the upper header especially)
Blue frame on the left nav looks ugly too and makes design look heavy.
Also I would remove exessive box shadows and maybe even chequered background.
But... maybe I'm just a big fun of light and unobtrusive design. =)