You wouldn't really be doing anything with that approach tbh Derek, neither giving improved cleanliness nor much visual difference, save from maybe moving a bit of dirt around.
The same approach with an encapsulation product would maybe facilitate more physical removal of soiling, depending on how well it actually lifts the soiling and also how well the post-vac was performed.
In cases like Mike describes above, where "knowing it's clean" is required rather than improving the looks, I would use a colloid (e.g. M-Power or Nemesis) sprayed quite liberally and agitated with a Minitex, using the tampico brush. Then I'd leave it to dry naturally to maximise the working time of the product.
I've also had some good successes using M-power with that technique (after a very extensive pre-vac) for dealing with mildew, dog and tobacco odours.