Would you upgrade your strobe or your snoot?

You would be hard pressed to do better than the Backscatter MF-1+Snoot package. It is by far the best and easiest snoot you can use in my experience. It's a strobe explicitly designed with the snoot in mind, and it aims perfectly. It's small enough to be very easy to manipulate. I have a 6 inch bungie with a bolt snap on the snoot, and leave it clipped to a zip tied o-ring on the ball mount. I can pop it off and leave it dangling and reattach without fumbling with it. If you can buy it on sale, it's a great deal. 

Size wise it seems the BS MF is much smaller and weights less, however as mentioned by you it is cumbersome due to extra optical cables and mounting it on the tray.

Marelux:

BS MF:

• Dimensions With Ball(LxWxD):
  • 7.36 x 2.31 x 4.06in
  • Weight in Air: 13.25oz/375g
  • Weight in Water: 5.29oz/150g