kryzak,
Whether admissions consultants are simply glorified editors or not, they do get exposed to thousands of B-school applications every year. This exposure and the learnings they derive from it can be quite useful because they would be able to benchmark your candidacy better. I think admissions consultants are useful for 2 specific aspects of the application.
Portfolio selection & Essay Editing
Unrealistic portfolio selection is probably the primary reason why applicants get dinged across the board. A good admissions consultant should be able to help with sensible advice for school selection.
Essay editing services are not unique to admissions consultants. There are 2 components to essay editing. Positioning and Prose. Any english editor can help you with prose, but an admissions consultant can potentially make a difference to your candidacy by helping you objectively evaluate the depth of your essays and by helping you focus on the specifics of an application. Also, an admission consultant has a vested interest in your success because successful client testimonials are valuable marketing tools.
In my view, the B-school admissions crap shoot is like learning to play the music.
Some consultants give you verbose text on what the parts of the violin are, how to play the right notes and even play tapes of memorable concerts. But, that still doesn't help you. Dont blow $5000 on these useless blokes.
The best consultants give you the violin from the get go, ask you to play, rebuke, teach, correct and repeat this cycle until you can create your own symphony. Good consultants share their experiences from when they learnt to play and can relate to you psychologically. Thus, they can probe you deeper than others and help you in the introspection process.
Simply put, there are crappy admissions consultants out there but there are also numerous good ones. Do your research well and dont rush in with the expectation that hiring an admissions consultant will automatically put you in B-school.
ozmba gave you 1 perspective. I wanted to give you another.