I had a acoustic bass for a few years, admittedly not a top-notch one, but it certainly made me realise that they're [i]very[/i] limited in their application.
Great for noodling at home without an amp, but useless unamplified against anything execpt a lightly fingerpicked guitar.
If you like the piezo sound, or the look, then go for it, but in my experience they lack more than they have.