Fuel Filter

I've got a '99 Ford Ranger P/U 4.0L with about160K miles. I live in San Diego, CA. At 127K miles I replaced the fuel filter. However, I'm not really sure when I should replace it next. The Scheduled Maintenance in my owner's Manual indicated that in California it was not mandatory to replace the filter. I have an OEM Ranger Repair Manual and I couldn't find any reference to the frequency of the replacement. In Haynes and Chilton OTC Repair Manuals, one stated it is not required and the other listed at 30K intervals. It just makes prudent sense that the fuel filter will need to be repalced. What do you think should be a reasonable interval. Of course most any Ranger owners know that the filter is located outside the vehicle right under the drivers side as opposed to being located in the gas tank with the fuel pump.

Follow Up: I've decided to go ahead and replace the fuel filter since I already bought one. I've talked to three mechanics and all suggested to replace them after 45-50K miles.