I'm in the same position as you blackrb20silvia... My fresh r32 gts-t import has a fair few mods and stuff done to it but is still running the standard ECU as far as I know. I've been tossing up between getting it remapped, or going straight for the AP Engineering ApeXi Power FC (Which I'll need one day anyway, and will provide better tune-ability than the factory ecu)
They way I figure it... I can either get the factory ECU remapped ($700 or so) or buy the Power FC ($1150 without handcontroller) + maybe $600 for tuning. If you plan on upgrading the ECU anyway I reckon you're better off going straight for an aftermarket one, otherwise you're effectively throwing $700 out the window. I'm in the process of getting quotes for the Power FC install and tune, as i'm leaning towards this option.
Edit: There's an article in a Zoom magazine I have (All about tuning and upgrading your r32 gtst. stock->160rwkw->220rwkw->250+), says the factory ECU can still be used for up to 220rwKW, but you'll need something like a Z32 airflow metre to go with it? I'm not too sure here, bit beyond my level of experience