SAFCs will have minimal effect on your economy, as when you are cruising (closed loop) the ECU reads the O2 sensor and constantly adjusts to achieve the preset mixture. The SAFC will save you some fuel when you are hard on the throttle (open loop), where it uses the air flow meter signal. A lot of tuners won't even bother to tune the low throttle map on the SAFCs, as mine did.
http://www.hondahookup.com/forums/showthread.php?t=92218
Other than an aftermarket ECU the best thing to do is make sure your engine is running as efficient as possible, ie new platinum plugs, new fuel filter and pump, new air filter, new O2 sensor, splitfire coil packs and drive 'off boost' whenever possible.