I agree with most of your points, but Im curious about why you think starch plays such a large role in the kinetics of kavalactone solubility. Sugars are still very polar, and if it's occupying hydrogen bonds, it's more likely to decrease the aqueous solubility of other solutes. by your logic, adding starch or sugar would theoretically increase the solubility of kavalactones. Also, it will not decrease the polarity of water. That is an inherent property.
The reason why nonpolar colloids, micelles, and liposomes can increase the solubility of kavalactones is because the nonpolar molecules are directly interacting with the kavalactones to solubilize them.
As far as why subsequent washes don't give you as much kavalactones as the math you suggested, it's due to solvation kinetics and cell biology. Some of the kavalactones are probably in a less accessible part of the cell or they could be protein bound. Also, the kinetics for dissolution are dependent on the concentrations of your solute and solvent. As you decrease the concentration of your kavalactones, you will dissolve them more slowly.
I promise I'm not trying to be an A-hole and I agree with most of your points! I'm just not following your logic for why starch is so important for increasing the aqueous solubility of kavalactones.