i asked myself this very question.
did some searching, talked with a few people.
this specific wire has a high amp rating, and it does this for a reason.
when the starter engages, its producing alot of torque to crank these engines at the correct speed.
in a motor, power in directly effects power out.
the solenoid of which you speak is a redundancy.
and you will not need it.
until you burn your starter solenoid wire in the middle of nowhere with nothing around -20 w/ wind chill.
a 30 dollar part seems like a really really good idea.
yes the starter motor has its own 12V supply, but to trigger it takes alot of work too.
im running one even with a powermaster.