@Sparx can this be fixed ?
Asking if it can be "fixed" is a statement that you believe it is "broken". Something that I don't agree with.
Can we write a UI that allows the flexibility of SQL without writing SQL? Probably not.
Can we satisfy all our users with something less than that? No chance. (Although allowing SQL is a way that the limitations of our UI don't mean something is impossible.)
Yes, extending to tagged values to the UI would still be nice. On the other hand it's among the simplest SQL to write and still has complexities for things like multiple tags with the same name.