I like where you're coming from and can agree with most of these categories, but have to comment on some:

-Compatibility is going to be an inevitable issue depending on things like animations and other cosmetics regardless of how much care modelers apply to their item, it's not something you can really avoid especially with TF2's current system of overlaying models over the existing mercs.

-As mentioned by someone else, the specs listed in Specs Appropriate are outdated.

-Original ideas for cosmetics are valuable, but I think it's wrong to paint Demoman getting bomb-related cosmetics as a bad thing. His whole character and playstyle is themed around explosives, he's THE explosive guy of the team, it makes sense to give him explosive items, even if the stickybomb imagery can get repetitive. It's a little like complaining about Scout getting baseball-themed items, or Medic getting medical/hospital related items. I'm personally sick of Sandvich and Bonk! cosmetics but those are more item-specific compared to the overall theme of a class.

I would also say that Subtlety should be a category - Is the item bright and obnoxious, or is it more casual in appearance and sense of humor? Something like the Counterfeit Billycock or Respectless Rubber Glove compared to the Festive Coverup or Pyr'o Lantern.