Unless your speakers are very sensitive, hum is not a problem and there's no need for the DC filament supply.
I think the shunt-regulated driver mod is a more audible improvement.
The stepped attenuator does make an improvement in the sonics. Note that it eliminates the balance control, but maintains more consistent balance as a function of gain setting, so kind of a mixed bag there.
My two cents; not everybody hears the same things in the same way, YMMV, etc.