How about using tags/links to associate attributes with requirements? This could be as simple as adding a link, fo e.g. :

• If it is traceable or not
  • [[attributes/traceable]]
  • [[attributes/untraceable]]
• Its criticality level
  • [[attributes/level/critical]]
  • [[attributes/level/important]]
  • etc.
• Its priority
  • [[attributes/priority/low]]
  • [[attributes/priority/high]]
• If it is functional or not
  • [[attributes/functional]]
  • [[attributes/non-functional]]

You just have to create pages for each attribute you want and then pagespec could be used to filter requirements by attributes. I think something similar is used to trac bug with ikiwiki (linking to a [[done]] page, etc.).

Generally speaking, I think it's always a good idea to get back to the "basics" for something, that huge and expensive tools were made for. But I'm doubtful if such a text oriented tool would really fit all needs of a requirements engineering tool... so what is your real world experience with your requirements engineering tool as described?