One vote here for Thought 1, unless under specific speed control. Constantly trying to keep the exact speed using thrust and speedbrake is a waste of energy (both yours and that of the aircraft). I find it usually (on the 777, but the idle descent logic is the same) averages out pretty well in the end if you just leave it alone. Forcing a path recalculation isn't going to change much for an idle profile with everything else remaining unchanged.
If you need to maintain the speed, intervene and use VNAV SPD. You can fix the profile if necessary as you get closer to the constraint.