G'day rokraider, enjoying your experimentation.
Zigzagging downwind only helps planing hulls, that are designed to exceed wind speed. For example, the Aussie 18 footer skiffs. These never sail straight downwind. Booming out the sail as you have done is the best downwind option, particularly in lighter winds.
I must admit to having thought about a boom for upwind sailing - only in my mind though, as I don't have my TI yet. However... this would work only if you limit the amount of mast bend with a forestay, and possibly side stays. Preventing the mast bend stops the top of the sail from twisting and depowering - which I might add is a design feature. Once you reduce the mast bend, the boom should be hauled down, to induce a flatter sail profile and shift the CE forward.
Bear in mind that this adds a lot
more stress to the rig though. The TI, for example, was apparently designed with the view to adding an optional jib, but Matt has advised that they struck some problems with the strength of the bow fitting - this probably applies to the AI as well. The mast base would also be subject to a lot more compressive force, but Matt didn't make any mention of this being a problem when the jib-equipped TI was trialled.