Sorry for the crickets.... had i been on yesterday i wouldn't have let them out.
Yes, the HPR readout on the ScanGauge is for the current horsepower use, although it's solely based on the specifications of the engine of the car it's connected to when you set up the scangauge. But there's a good chance that it's pretty accurate, too.
As far as thoughts on low RPM power.... from a 451, pretty sure the only way you'd get that without the already mentioned transmission modifications (are they even a thing for a ForTwo? Have people actually done that?), is by turbocharging it. Assuming you have a 451, based on your pic, according to the specs you don't hit peak horsepower until about 5,800 RPM's or peak torque til about 4,500. Compare that to a 453 which has a .9L turbo, and it doesn't hit peak horsepower until a bit higher than that.... 6,200 RPM's (probably due to the ever so slightly smaller engine), but its peak torque hits at about 2,500 RPM's.
I'm not the MOST knowledgeable on the subject.... so hopefully someone else comes around to keep the crickets at bay.... but basically as far as i'm aware, having some sort of forced induction system on a car, be it a turbo- or supercharger, is the BIGGEST way to see a drastic bump in low RPM performance. Also probably why the 451 is only rated for 68 lb-ft of torque, while the 453 is rated for 100 lb-ft.