FWIW, there isn't much instrument training for your private certificate. You basically just need to be able to understand VOR navigation, manage attitude and speed, and navigate based on instructions from the tower using your instruments.

They pretty much want to give you the skills needed to get help and get back on the ground if you find yourself in a bad situation. And to not overreact and stall or spin yourself into the ground because you didn't trust the instruments.

With that said, there isn't such a thing as knowing too much about flying. But if your aircraft isn't IFR equipped (and lots of rentals aren't), you won't be able to practice much more than the above.