As someone who has read nearly every thread on Gore's Great World Wide Web about record cleaning, and through my own experience, there are a few things I think I'm pretty confident about enough to state:
1. Brushes don't get down in grooves - they may follow a groove in the big picture, but the bristles aren't small enough to get down into where the gunk is. They do serve a purpose in spreading the fluid around, and in agitating it.
2. It's the solution that separates the gunk from the grooves. Finding the right solution for the gunk is the challenge. For 80% of the records I clean, my home made solution of distilled water, 91% IPO, and a drop of Dawn does great. Most of the rest can be cleaned with the Audio Intelligence one step cleaner, and letting it soak in to allow the anti-enzyme agents work. In rare cases I get out the 3 step solution.
3. The final steps are key: Rinse with pure/distilled water spread with a dedicated brush, and VACUUM the solution.
I've done the hand washing with dent pullers and the spin clean and both work to make dirty records cleaner. Spin clean a step above the hand washing, but my VPI 16.5 is 14 steps above either.