I think you're going to find yourself wanting a larger case, or smaller modules... you're going to want more modulation sources.

For the original question: it's a toss up. You get a little added flexibility from the Duatt, at the expense of some of the features of the other VCA. I would go the Duatt/VCA route myself.

Finally, another unsolicited thought. You don't have anything here that makes use of the Palette's I/O or midi... which basically means you're overpaying for a very small case. The portability of the Palette is great... but think about how much cooler this system would be if you just picked up a 104 hp skiff, replaced the 1u modules with 3u versions (18 hp), then still had 24 hp of space to play with?