Is this just a gimmick or can it actually have some positive effect on a coupe's performance?

Grrrrreddy

I have no knowledge of this kit but I'd say it's a complete gimmick. It's amazing what the jap tuning crowd will make if there's a quick buck in it

looks just like a capacitor to me ?

Most likely!

lets face it, for 30$ you may end up with better ICE system, which is not that bad after all . Now about stabilising current to ECU and improving readings etc looks like bull to me...

I dont know. Electronics can be sensitive to voltage changes, I dont see any reason why the ECU should be any different.

Greddy are not know for making products that are a load of crap!....

I'd expect that since ECU is THE most important bit of electronics in an automobile, the designer would have taken care of stabilizing currents, avoiding spikes that may be caused from anything, etc etc. That's why I don't really see the point.