I finally made the move this morning to drain my Platinum CashPlus account and just pay the $55 per month service fee. In addition to the foregone (now) 3.85% APY at Bask Bank, MS 1099-ing the $695 engagement bonus moves the needle enough to make the change worthwhile. My arithmetic for the after tax comparative costs of the three Amex Plat + AU options, assuming my 33% combined federal and state nominal income tax rate tier….
Option 1) No MS account: $695 primary + $175 AU = $870
Option 2) MS CashPlus $25,000 monthly average: $25,000 x 3.85% x 67% (foregone after tax interest) + $695 x 33% (tax on engagement bonus) = ~$874
Option 3) MS CashPlus $0 monthly average: $55 (monthly account fee) x 12 + ($695 - $55 x 12) x 33% (net tax on engagement bonus) = ~$672
In summary, all of the Morgan Stanley machinations save me ~$198 per year for a MS Plat versus a Vanilla Plat. Hardly seems worth it after the first year of card membership.