As usual, some brilliant and generous soul has come up with something better than I could hope for:
http://www.macdrifter.com/2014/02/application-buckets-with-alfred-and-tags.html
The brilliant part is that it searches by TAGS. And since an application can have several tags, it makes a very flexible system for say showing graphics apps and PDF apps, even though there'd be overlap.
Pay attention to the info about adding system tags to applications; I still think it can't be done in Finder. But I use Path Finder as he suggested.