Sure, I use open strings. They have a different sound than a fretted note. And in fact, even fretted equivalent notes have different sounds (eg B played on the 7th fret of the E string vs 2nd fret of the A string). I don't know that I'd call the nut a crutch - if anything it often is harder to include those notes as when you're up the neck you're playing patterns that tend to not vary.
As for control, you've got two hands
. Both hands play into shaping the sound. Your left hand can fret a note, hammer on, pull off, pluck a note, and also damp a note. Your right hand can pluck, slap, pop, tap, palm mute, and totally mute a note. Lots of things at your disposal. If you ignore any of those then you're removing tools from your tool box.
One thing that both Kai and Anthony insisted was that you know the bass - as in really know the bass. You should know where every Bb is on the instrument instantly. There are things that need to be automatic. Once you know those, then they get out of the way of you actually making music. I'm still working on that stuff every day (mostly getting my modes instant and seamless).
If you're staying around the 5th and 7th frets, then you're not getting your money's worth out of the instrument. While the saying goes, "there is no money above the 7th fret", there are colors up there that can serve a lot of songs if they are used correctly. Same with open notes. Music is a never ending exploration and is only limited by your imagination.