To the OP. I have a Tsunami Cap in my wife's car. Honestly? It's the same as pretty much every other cap. It just has pretty flashing lights.
I also have a Cap in my car.
Why do I have Caps? Here's my reasoning. I didn't upgrade the alternators, but I did upgrade the grounds under the hood. In my car, I have 4Ga running everywhere from the battery. THAT, helped. Having real solid grounds under the hood instead of the stock 12ga to the bumper helped a LOT.
Unfortunately, my problem comes in at IDLE with the headlights on. This is the ONLY time anything in my car dims. My headlights take a LOT of power.
And y'know what, the Cap helped soften that. At least as far as the subs (on tight, frequent notes) would drag down the system. Is it a perfect solution? No. But, I know people who have upgraded alternators that STILL had a problem of lights dimming at IDLE.
My car is fine when it's at speed (2k rpm or higher), so if i'm moving, I wouldn't need the cap. I only have the cap to soften the blows when i'm sitting still.
I have no scientific data. I don't claim to be intelligent, i'm just stating my situation and what I did. Is it a band-aid? Maybe. Am I guaranteed that a higher-output alternator would fix my problem at Idle? Not really.
That's just me.