Backtrolling is a technique that seems to have been mostly made redundant by our electric motors and big batteries. Mine will run for days at 1-1.5 mph.
I can see the appeal of planer boards for picking up scattered fish on big flats. We don't really have much of that here, so I've never tried them. I also saw them as a big mess waiting to happen, especially if you're fishing solo.
From what I have heard recently, the latest live imaging is better, but not by much. You aren't missing out on much if you don't decide to wait. At some point you have to draw the line at just how much you want to spend to catch a fish, and if you're walleye fishing, you will find it's usefulness to be somewhat limited because of their habits (often right on the bottom where you can't see them.)