Prior to my ownership, in the first 3 years, oil & filter changes were completed at the following mileage intervals, 545, +1101, +383 & +1131. Using an engine flush would certainly have been a waste of money over those distances.
Over the last 7 years, the oil & filter has been changed at various mileage intervals of between 3,319 & 6,870 miles. (The latter being one exception, all others were at 6K or less). If I do decide to half the service intervals, then I might just add a one off engine flush then just continue with the reduced mileage intervals.