Yeah, for me the main thing is I'm very unlikely to play a bass over my Cbass. I've tried a handful of other Birdsongs and I always come back to the Cbass, which leaves me with an approximately $2k bass that I don't tend to use.That's the way I went. Mine are both walnut bodied with rosewood boards, but with different pickguards. I'm really happy with them, especially when switching from one to the other.
On the other hand, I really think it's worth having a reliable back up at gigs in case something were to happen (broken string for example). The shortbass would be perfect for this. I also love playing fretless, though I'm not very good at it and don't have a real gigging use for it. Again, the shortbass would be perfect to fill this little niche in my life.