Couple of things Justin.
I don't have a rotovac, so my advice may be way off the mark. Good use of the correct chemicals, adequate dwell time and good agitation are the key on traffic areas. You could use an Envirodri or alternate CRB machine, a rotary or even a good old grandi groomer hand rake, I use them all and each have their place but it is the distribution of the chemical to fibre and contact time which are the key. I've done some terrible black top with hot powerburst, 15 min dwell and rotary with brilliant results. Bare in mind also traffic areas by their very nature have taken much more traffic, wearing fibres, bending and twisting them so light is deflected rather than reflected. This would appear to make the carpet have darker patches or traffic lanes because it's opposed to how the pile naturally lays in adjacent areas. Most domestics I use a standard M/S or Chemspecs DFC 105 as pre spray, 10mins dwell and a carpet rake, rinse with warm water. Now trying Fusion 8 with some very pleasing results.
Commercially a rotovac would make sense if your cleaning large areas, domestically get the best agitation machine you can afford and do the work before the rinse.
Cheers
Simon