Lightened flywheel is a worthwhile upgrade as well.
Yeah, more so than a lightened crank.
The flywheel makes a noticable difference...the crank will make no difference if you bolt it to the damn great lump of pig iron that is the standard flywheel.
The standard VR6 crank is not badly balanced as it is, so little need to mes with it.
It's perfectly fine up to 7500 RPM, and to be making power up there you will be into different cams anyway...so on a standard engine, no point in messing with it.