Well, new plugs aren't going to affect the ECU/fuel trims unless the old plugs were fouled out and missfiring. However, it won't hurt anything to reset the ECU either, Whatever makes you happy...
The miles isn't the key to the ECU learning, it is a complete drive cycle which in volves two cold start-ups. However, the ECU is pretty much done with fuel trims after 20 or so miles of stop/go in-town type driving with at least one WOT trip up the tach.