"... and when you use all this low pass/high pass stuff, it doesn't really matter what the "solo'd" track sounds like -- only what it sounds like in the overall mix"

I see your point, and in that regard it's true.
However soloing the track can still help at times. I've had times when I was trying to fix a bass sound, and found the problem was actually on the low E string of the guitar.

Make your sound your own!
.. I do not work here, but the benefits are still awesome