Generally, when good auction grade (4 and above) used JDMs are imported here, they do not require any such activity irrespective of mileage / odo reading. Fuel quality is far better there. They only start getting clogged after being driven here for at least 10-15,000 Kms.
Secondly, if there is drop in fuel economy along with pick and power, then there may be issue with Catalytic Converter, otherwise, if you are just facing reduced fuel economy but pick, power, etc. is great, then no need to mess with it.
Cause for reduced fuel economy can be something else, other than just clogged Catalytic Converter.