That adds to the appearance, no doubt, but it's still ground-in dirt that causes most of the unpleasant look in a lot of cases.
Lots of agitation between spraying and extraction will definitely help, but it's hard for anyone to say how much of a difference without seeing the specific job at hand. You might find a brush attachment much more useful than a bonnet at this stage.
Is this a domestic or commercial job? If it's commercial low-profile, you can minimise the risk of wicking by using your bonnet machine. After extraction, allow the carpet to partially dry and go over it again with a clean bonnet. A light spray of non-detergent solution can often help out at this stage before you bonnet, to give a little lubrication and remove a bit more soiling.