I think people are quick to spend others money, If the exhaust is in good shape I see no reason to replace it. Theres really no difference in a pair of 2.25" flowmaster or a pair of 3" flowmasters other then the size of the pipe going in it.
They are chambered mufflers and the chambers dont change with inlet size so to replace the mufflers with another pair of Flows is a waste of money to me. He would be slowing down the exhaust gasses with smaller pipe but pretty much be feeding them in to the same muffler. It may bring torque up a bit but not enough to be worth the investment unless he find a shop willing to do it real cheap and can sell the old system to offset the cost.
I bet a bit of time spent on ignition and carb tuning would bring his toque to were it should be.